House of Roman - HackTricks

# House of Roman

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## Basic Information

This was a very interesting technique that allowed for RCE without leaks via fake fastbins, the unsorted_bin attack and relative overwrites. However it has ben patched.

### Code

- You can find an example in https://github.com/shellphish/how2heap/blob/master/glibc_2.23/house_of_roman.c

### Goal

- RCE by abusing relative pointers

### Requirements

- Edit fastbin and unsorted bin pointers
- 12 bits of randomness must be brute forced (0.02% chance) of working

## Attack Steps

### Part 1: Fastbin Chunk points to __malloc_hook

Create several chunks:

- `fastbin_victim` (0x60, offset 0): UAF chunk later to edit the heap pointer later to point to the LibC value.
- `chunk2` (0x80, offset 0x70): For good alignment
- `main_arena_use` (0x80, offset 0x100)
- `relative_offset_heap` (0x60, offset 0x190): relative offset on the 'main_arena_use' chunk

Then `free(main_arena_use)` which will place this chunk in the unsorted list and will get a pointer to `main_arena + 0x68` in both the `fd` and `bk` pointers.

Now it's allocated a new chunk `fake_libc_chunk(0x60)` because it'll contain the pointers to `main_arena + 0x68` in `fd` and `bk`.

Then `relative_offset_heap` and `fastbin_victim` are freed.

    /*
    Current heap layout:
    	0x0:   fastbin_victim       - size 0x70
    	0x70:  alignment_filler     - size 0x90
    	0x100: fake_libc_chunk      - size 0x70 (contains a fd ptr to main_arena + 0x68)
    	0x170: leftover_main        - size 0x20
    	0x190: relative_offset_heap - size 0x70

    	bin layout:
    			fastbin:  fastbin_victim -> relative_offset_heap
    			unsorted: leftover_main
    */

- `fastbin_victim` has a `fd` pointing to `relative_offset_heap`
- `relative_offset_heap` is an offset of distance from `fake_libc_chunk`, which contains a pointer to `main_arena + 0x68`
- Just changing the last byte of `fastbin_victim.fd` it's possible to make `fastbin_victim points` to `main_arena + 0x68`

For the previous actions, the attacker needs to be capable of modifying the fd pointer of `fastbin_victim`.

Then, `main_arena + 0x68` is not that interesting, so lets modify it so the pointer points to `__malloc_hook`.

Note that `__memalign_hook` usually starts with `0x7f` and zeros before it, then it's possible to fake it as a value in the `0x70` fast bin. Because the last 4 bits of the address are random there are `2^4=16` possibilities for the value to end pointing where are interested. So a BF attack is performed here so the chunk ends like: `0x70: fastbin_victim -> fake_libc_chunk -> (__malloc_hook - 0x23)`.

(For more info about the rest of the bytes check the explanation in the how2heap example). If the BF don't work the program just crashes (so start gain until it works).

Then, 2 mallocs are performed to remove the 2 initial fast bin chunks and the a third one is alloced to get a chunk in the `__malloc_hook:`

    malloc(0x60);
    malloc(0x60);
    uint8_t* malloc_hook_chunk = malloc(0x60);

### Part 2: Unsorted_bin attack

For more info you can check:

Unsorted Bin Attack

But basically it allows to write `main_arena + 0x68` to any location by specified in `chunk->bk`. And for the attack we choose `__malloc_hook`. Then, after overwriting it we will use a relative overwrite) to point to a `one_gadget`.

For this we start getting a chunk and putting it into the unsorted bin:

    uint8_t* unsorted_bin_ptr = malloc(0x80);
    malloc(0x30); // Don't want to consolidate

    puts("Put chunk into unsorted_bin\n");
    // Free the chunk to create the UAF
    free(unsorted_bin_ptr);

Use an UAF in this chunk to point `unsorted_bin_ptr->bk` to the address of `__malloc_hook` (we brute forced this previously).

> [!CAUTION] Note that this attack corrupts the unsorted bin (hence small and large too). So we can only use allocations from the fast bin now (a more complex program might do other allocations and crash), and to trigger this we must alloc the same size or the program will crash.

So, to trigger the write of `main_arena + 0x68` in `__malloc_hook` we perform after setting `__malloc_hook` in `unsorted_bin_ptr->bk` we just need to do: `malloc(0x80)`

### Step 3: Set __malloc_hook to system

In the step one we ended controlling a chunk containing `__malloc_hook` (in the variable `malloc_hook_chunk`) and in the second step we managed to write `main_arena + 0x68` in here.

Now, we abuse a partial overwrite in `malloc_hook_chunk` to use the libc address we wrote there(`main_arena + 0x68`) to point a `one_gadget` address.

Here is where it's needed to bruteforce 12 bits of randomness (more info in the how2heap example).

Finally, one the correct address is overwritten, call `malloc` and trigger the `one_gadget`.

## References

- https://github.com/shellphish/how2heap
- https://github.com/shellphish/how2heap/blob/master/glibc_2.23/house_of_roman.c
- https://ctf-wiki.mahaloz.re/pwn/linux/glibc-heap/house_of_roman/

> [!TIP] Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
> Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

> Support HackTricks
> - Check the subscription plans!
> - Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.
> - Share hacking tricks by submitting PRs to the HackTricks and HackTricks Cloud github repos.