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</details>
## **Malloc Hook**
As you can [Official GNU site](https://www.gnu.org/software/libc/manual/html\_node/Hooks-for-Malloc.html), the variable **`__malloc_hook`** is a pointer pointing to the **address of a function that will be called** whenever `malloc()` is called **stored in the data section of the libc library**. Therefore, if this address is overwritten with a **One Gadget** for example and `malloc` is called, the **One Gadget will be called**.
To call malloc it's possible to wait for the program to call it or by **calling `printf("%10000$c")`** which allocates too bytes many making `libc` calling malloc to allocate them in the heap.
Note that hooks are **disabled for GLIBC >= 2.34**. There are other techniques that can be used on modern GLIBC versions. See: [https://github.com/nobodyisnobody/docs/blob/main/code.execution.on.last.libc/README.md](https://github.com/nobodyisnobody/docs/blob/main/code.execution.on.last.libc/README.md).
A nice trick (from [**here**](https://guyinatuxedo.github.io/41-house\_of\_force/bkp16\_cookbook/index.html)) to find the location of the free hook if the binary has symbols is to **do something like**:
```
gef➤ set __free_hook = 0xfacade
gef➤ search-pattern 0xfacade
```
In the same post you can find a step by step guide on how to locate the address of the free hook without symbols. As summary, in the free function:
* If we manage to get a fast chunk of size 0x200 in this location, it'll be possible to overwrite a function pointer that will be executed
* For this, a new chunk of size `0xfc` is created and the merged function is called with that pointer twice, this way we obtain a pointer to a freed chunk of size `0xfc*2 = 0x1f8` in the fast bin.
* Then, the edit function is called in this chunk to modify the **`fd`** address of this fast bin to point to the previous **`__free_hook`** function.
* Then, a chunk with size `0x1f8` is created to retrieve from the fast bin the previous useless chunk so another chunk of size `0x1f8` is created to get a fast bin chunk in the **`__free_hook`** which is overwritten with the address of **`system`** function.
* And finally a chunk containing the string `/bin/sh\x00` is freed calling the delete function, triggering the **`__free_hook`** function which points to system with `/bin/sh\x00` as parameter.
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