hacktricks/reversing-and-exploiting/linux-exploiting-basic-esp/arbitrary-write-2-exec/aws2exec-.dtors-and-.fini_array.md

# AWS2Exec - .dtors & .fini\_array

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## .dtors

{% hint style="danger" %}
Nowadays is very **weird to find a binary with a .dtors section**.
{% endhint %}

The destructors are functions that are **executed before program finishes** (after the `main` function returns).\
The addresses to these functions are stored inside the **`.dtors`** section of the binary and therefore, if you manage to **write** the **address** to a **shellcode** in **`__DTOR_END__`** , that will be **executed** before the programs ends.

Get the address of this section with:

```bash
objdump -s -j .dtors /exec
rabin -s /exec | grep “__DTOR”
```

Usually you will find the **DTOR** markers **between** the values `ffffffff` and `00000000`. So if you just see those values, it means that there **isn't any function registered**. So **overwrite** the **`00000000`** with the **address** to the **shellcode** to execute it.

{% hint style="warning" %}
Ofc, you first need to find a **place to store the shellcode** in order to later call it.
{% endhint %}

## **.fini\_array**

Essentially this is a structure with **functions that will be called** before the program finishes, like **`.dtors`**. This is interesting if you can call your **shellcode just jumping to an address**, or in cases where you need to go **back to `main`** again to **exploit the vulnerability a second time**.

```bash
objdump -s -j .fini_array ./greeting

./greeting:     file format elf32-i386

Contents of section .fini_array:
 8049934 a0850408

#Put your address in 0x8049934
```

Note that this **won't** **create** an **eternal loop** because when you get back to main the canary will notice, the end of the stack might be corrupted and the function won't be recalled again. So with this you will be able to **have 1 more execution** of the vuln.

{% hint style="danger" %}
Note that with [Full RELRO](../common-binary-protections-and-bypasses/relro.md), the section `.fini_array` is made **read-only**.
{% endhint %}

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