Libc-GOT-Hijacking

Transform arbitrary write to RCE.

This repo provides an idea that performs ROP on GOT and demonstrates its ability (even most people would never use it because of the existing simple method). Also, this repo shows an ignored fact: writable libc got is useful for exploitation.

This is a userspace attacking skill: If you can write arbitrary memory space, you can use this method to execute arbitrary code.

The simplest way to attack is to find a function using writable GOT value and set it system to perform system("/bin/sh"). It depends on the challenges/cases and it's good enough for most cases and this repo is giving a more complex/verbose solution to gain not only RIP but ROP for generic cases.

1. You only need to know the base address of Glibc.
2. Libc makes it full RELRO at 2.39 so this skill doesn't work for glibc-2.39+.
3. However, it works for the libstdc++ on the latest Ubuntu LTS.

Before Reading

This repo is a generic solution to gain Code Execution (ROP level).

• You don't need this repo unless
  • You just want a generic solution without spending time debugging a specific case
  • You need ROP instead of system("/bin/sh").

For most simple cases, the simple solution is:

• Hijack one got entry (<=6 bytes write)
• Find a trigger function for which the parameters are nice.
  • Case 1: The trigger function takes controllable parameters. (e.g., some_func(str)). We set some_func's got to system.
  • Case 2: The trigger function takes stack pointers (in a retunable function stack frame) as the first parameter. -> We set it to gets to get a buffer overflow.

Update

• Dec 17th., 2024 While exploiting a CTF challenge, I found libstdc++ is a juicy target of this technique. It's still usable on the latest LTS-ubuntu(24.04).

[14:26:12] n132 :: xps  ➜  ~/Downloads/FL_Support_Center » pwn checksec /lib/x86_64-linux-gnu/libstdc++.so.6
[*] '/lib/x86_64-linux-gnu/libstdc++.so.6'
    Arch:     amd64-64-little
    RELRO:    Partial RELRO
    Stack:    Canary found
    NX:       NX enabled
    PIE:      PIE enabled
    FORTIFY:  Enabled

A simple way to get a shell is just to modify fread/fwrite got to system and cin/cout the string /bin/sh. But if ROP is what we want, we can do libc-got-hijacking (ROP over GOT) (even though it's unnecessary, it's a general solution!)

Here is a demo (https://asciinema.org/a/krgiZ9HEX633nOhgT86OJy3aH)

[18:34:04] n132 :: xps  ➜  ~/demo » cat ./rce.cpp && g++ ./rce.cpp -o ./rce && echo "id" | ./rce
#include <iostream>
int main(){
    // Hijack fwrite@got[plt] to system
    // cout gonna run arbitrary commands
    int num = 915;
    std::string str;
    size_t libc_base = (size_t)system-0x00058740;
    size_t * add_of_del_got = (size_t *)(libc_base + 0x277000 + 0x400000 + num*8);
    * add_of_del_got = (size_t )system;
    std::cin >> str;
    std::cout << str << std::endl;
}
uid=1000(n132) gid=1000(n132) groups=1000(n132),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),100(users),114(lpadmin),984(docker)

glibc (2.36-2.38)

Compared to glibc<=2.35 there is mitigation implemented, which forbids the methods for the old library. However, we designed a method to bypass it and execute arbitrary code by once arbitrary write on Glibc's GOT table. This method performs Return Oriented Programming (ROP) attack on the Global Offset Table (GOT).

You can find details, templates, demos, and everything you want in: Details and Templates

glibc (unk-2.35)

I learned the original method from Sammy Hajhamid also the methods for glibc <=2.35 are inspired by his work.

Based on his work, We designed a method to execute arbitrary code by once arbitrary write on Glibc's GOT table. The method uses PLT_0 to push libc_exe_address to the stack and then use POP RSP, RET to execute our ROPchain.

You can find details, templates, demos, and everything you want in: Details and Templates

Acknowledgments

• Great job @swing on the impressive work with glibc >2.35!

• Appreciate the original work done by @pepsipu.

Reference link

• @pepsipu's Method