iNarcissuss / kernelpwn

kernel-pwn and writeup collection

kernel pwn

About this repo

This repository collects CTF kernel-pwn challenges and writeups. Also, it introduces how to start learning kernel-pwn for beginners including me. All the challs here are solved by me, though the writeup may be based on the author's one or others's ones. I'm planning to include not only kernel-pwn, but also general non-userland pwn including QEMU, V8, multi-arch...

IMPORTANT: If you know some good kernel(non-userland) pwn challs, please tell me and I'll solve it. Then I'll add it on this repo if I feel it good to solve. And if you notice some wrong points in my writeups or blog posts, feel free to contact me.

Good Challs

• kone_gadget from SECCON CTF 2021

  • SMEP/ SMAP/ KPTI/ no-KASLR/ unprivileged ebpf installation is NOT allowed / well-crafted shellcode in JIT-ed seccomp filter
  • https://smallkirby.hatenablog.com/entry/2021/12/12/211601
  • you are able to control RIP but all the registers are zero-cleared before it. Unprivileged ebpf is forbidden, but seccomp filter is still JIT-ed. you abuse operand to be shellcode and jump everytime to next opcode (which means next shellcode).
  • Unexpected solution is jmp &flag, which leaks secret content in CODE secition of panic message. It means that if the kernel uses initramfs and KASLR is disabled (or we have full knowlege of memory layout), just getting RIP means success of exploit, SMEP/SMAP is useless.

• klibrary from 3kCTF 2021

  • SMEP/ SMAP/ KPTI/ KASLR/ race w/ uffd/ tty_struct/ modprobe_overwrite via vtable in tty_struct
  • https://smallkirby.hatenablog.com/entry/2021/12/05/132253
  • between beginner and med

• shared knote from Bsides Ahmedabad 2021

  • no-SMEP/ no-SMAP/ KPTI/ KASLR/ modprobe_path search/ invalid fpos use/ zero-addr mapping
  • https://smallkirby.hatenablog.com/entry/2021/11/07/140644
  • I added check /proc/sys/vm/mmap_min/addr in my first procedures list.

• pprofile from LINE CTF 2021

  • SMEP/ SMAP/ KPTI/ KASLR/ pointer validation/ modprobe_path
  • https://smallkirby.hatenablog.com/entry/2021/03/21/160134
  • I realized again that validating userland pointer is important and kernel can endure some wirte-bruteforce. If the validation doesn't exist in distributed binaries, I should recall this chall.

• nutty from Union CTF 2021

  • SMEP/ SMAP/ KPTI/ KASLR/ race without uffd/ SLOB
  • https://smallkirby.hatenablog.com/entry/2021/02/22/053507
  • NOTE: I ignored the heap-overflow bug, and invoked race condition w/o uffd to abuse tty_struct. Then, bypass SMAP by kROP in kheap(on tty_strut).

• Day One from AIS3 EOF CTF 2021 Final

  • SMEP/ SMAP/ KPTI/ KASLR/ eBPF verifier
  • https://smallkirby.hatenablog.com/entry/2021/02/20/131428
  • NOTE: the first half part of the chall is a little bit boring cuz it is exactly the same with the report of ZDI. But, the last half part, where we get root without bpf_map.btf, is cool.

• kernel-rop from hxp CTF 2020

  • SMEP/ SMAP/ KPTI/ FGKASLR/ single-core/ kROP
  • https://smallkirby.hatenablog.com/entry/2021/02/16/225125

• SharedHouse from ASIS 2020 Quals

  • SMEP/ no-SMAP/ no-KPTI/ single-core/ heap
  • https://smallkirby.hatenablog.com/entry/2021/02/13/230520

• Spark from HITCON 2020

  • SMEP/ no-SMAP/ no-KPTI/ signle-core/ heap
  • https://smallkirby.hatenablog.com/entry/2021/02/09/133655

• hashbrown from DiceCTF 2021

  • SMEP/ SMAP/ KPTI/ FGKASLR/ double-core/ race/ hardened-heap
  • https://smallkirby.hatenablog.com/entry/2021/02/15/215158

• gnote from TokyoWesterns CTF 2019

  • race
  • https://smallkirby.hatenablog.com/entry/2019/11/19/225504

• eebpf from TokyoWesterns CTF 2020

  • eBPF/ verifier bug
  • https://smallkirby.hatenablog.com/entry/2021/01/31/210158

• Krazynote from BalsnCTF 2019

  • classic uffd/ race
  • https://smallkirby.hatenablog.com/entry/2020/08/09/085028

Frequently Updated now...

Nirugiri

I don't know these challs are difficult or not and good or soso. But at least I feel these challs are worth solving.

• hwdbg from CakeCTF 2021

  • TODO: writeup
  • SMEP/ SMAP/ KPTI/ KASLR/ physicasl memory access/ modprobe_path
  • https://smallkirby.hatenablog.com/entry/2021/08/30/142639
  • You have AAW towards /dev/mem/, so all the protection is useless. However, CONFIG_DEVMEM_STRICT is enabled and you would be confused if you don't know this config.

• Stonks Socket from Hack.lu CTF 2021

  • no-SMEP/ no-SMAP/ race w/o uffd/ custom TCP hook
  • https://smallkirby.hatenablog.com/entry/2021/12/02/162758
  • challenge itself is a little bit buggy, but enough for practice of race w/o uffd.

Frequently Updated now...

Beginners

If you don't know how to prepare for solving kernel-pwn, please refer to start-kernel-pwning.

• lkgit(TBD) from TSGCTF 2021
  • SMEP/SMAP/KPTI/KASLR/race
  • simple uffd, though appropriate fault timing handling is required.
  • https://smallkirby.hatenablog.com/entry/2021/10/03/171804
• meowmeow from zer0pts CTF 2020
  • buffer overflow
  • https://smallkirby.hatenablog.com/entry/2020/07/23/221605
• kstack from SECCON CTF 2020
  • race
  • https://smallkirby.hatenablog.com/entry/2020/10/14/184245
• babydriver from NCSTISC CTF 2018
  • kUAF
  • https://smallkirby.hatenablog.com/entry/2021/02/14/110450
• flitbip from Midnightsun CTF 2018 Finals
  • no-SMEP/ no-SMAP/ no-KASLR/ custom syscall
  • https://smallkirby.hatenablog.com/entry/2021/02/14/142626

Frequently Updated now...

Techniques

I want to know some techniques to pwn in kernelland. If you know something I should know, please tell me. For the techniques I used to solve the challs listed above is listed HERE(under construction).

Frequently Updated now...

Configs to check

Kernel is distributed in the form of bzImage and no information about build configuration is not provided in 99% cases. However, you have to change the way of exploit depending on the configuration. Some config might hide important information. Some config might randomize the memory layout. Some config might make variables only readable... important_config directory collects the important configurations and tries to summarize how to check if it is enabled and how to bypass it.

My Blog

My blog posts contain not only kernel-writeup, but normal userland-pwn and technique frequently used in pwning and so on... Please check it out. NOTE: The most parts of my blog is written when I'm solving the chall as a memo in HackMD and is converted to blog entry with md2html converter . I received some DMs which ask me to write my blog posts in Englinsh and I'm willing to, cuz writing in English is not a so heavy task for me (regardless of the quality of my English). I know that my blog is ill-translated by Google translater :( I'm planning to write them in English someday in the near future.

References

List of usefull resources are listed under reference directory.

If you have any suggestions, feel free to contact me on Twitter.

DISCLAIMER

You can cite or use my code and comments in this repo as you like basically.
The exceptions are when the code belongs to some other licenses. In that case, follow them. Also, you can't use them for evil purpose. Finally, I don't take any responsibility for using my code or comment.
If you find something useful, or you notice that hoge is wrong, I'll appreciate if you leave comments via PR, Issue, DM, or Blog.