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53 lines
3.2 KiB
Markdown
53 lines
3.2 KiB
Markdown
# House of Einherjar
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{{#include ../../banners/hacktricks-training.md}}
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## Basic Information
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### Code
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- Check the example from [https://github.com/shellphish/how2heap/blob/master/glibc_2.35/house_of_einherjar.c](https://github.com/shellphish/how2heap/blob/master/glibc_2.35/house_of_einherjar.c)
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- Or the one from [https://guyinatuxedo.github.io/42-house_of_einherjar/house_einherjar_exp/index.html#house-of-einherjar-explanation](https://guyinatuxedo.github.io/42-house_of_einherjar/house_einherjar_exp/index.html#house-of-einherjar-explanation) (you might need to fill the tcache)
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### Goal
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- The goal is to allocate memory in almost any specific address.
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### Requirements
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- Create a fake chunk when we want to allocate a chunk:
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- Set pointers to point to itself to bypass sanity checks
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- One-byte overflow with a null byte from one chunk to the next one to modify the `PREV_INUSE` flag.
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- Indicate in the `prev_size` of the off-by-null abused chunk the difference between itself and the fake chunk
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- The fake chunk size must also have been set the same size to bypass sanity checks
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- For constructing these chunks, you will need a heap leak.
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### Attack
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- `A` fake chunk is created inside a chunk controlled by the attacker pointing with `fd` and `bk` to the original chunk to bypass protections
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- 2 other chunks (`B` and `C`) are allocated
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- Abusing the off by one in the `B` one the `prev in use` bit is cleaned and the `prev_size` data is overwritten with the difference between the place where the `C` chunk is allocated, to the fake `A` chunk generated before
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- This `prev_size` and the size in the fake chunk `A` must be the same to bypass checks.
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- Then, the tcache is filled
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- Then, `C` is freed so it consolidates with the fake chunk `A`
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- Then, a new chunk `D` is created which will be starting in the fake `A` chunk and covering `B` chunk
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- The house of Einherjar finishes here
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- This can be continued with a fast bin attack or Tcache poisoning:
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- Free `B` to add it to the fast bin / Tcache
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- `B`'s `fd` is overwritten making it point to the target address abusing the `D` chunk (as it contains `B` inside) 
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- Then, 2 mallocs are done and the second one is going to be **allocating the target address**
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## References and other examples
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- [https://github.com/shellphish/how2heap/blob/master/glibc_2.35/house_of_einherjar.c](https://github.com/shellphish/how2heap/blob/master/glibc_2.35/house_of_einherjar.c)
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- **CTF** [**https://ctf-wiki.mahaloz.re/pwn/linux/glibc-heap/house_of_einherjar/#2016-seccon-tinypad**](https://ctf-wiki.mahaloz.re/pwn/linux/glibc-heap/house_of_einherjar/#2016-seccon-tinypad)
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- After freeing pointers their aren't nullified, so it's still possible to access their data. Therefore a chunk is placed in the unsorted bin and leaked the pointers it contains (libc leak) and then a new heap is places on the unsorted bin and leaked a heap address from the pointer it gets.
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- [**baby-talk. DiceCTF 2024**](https://7rocky.github.io/en/ctf/other/dicectf/baby-talk/)
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- Null-byte overflow bug in `strtok`.
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- Use House of Einherjar to get an overlapping chunks situation and finish with Tcache poisoning ti get an arbitrary write primitive.
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{{#include ../../banners/hacktricks-training.md}}
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