# Use After Free {% hint style="success" %} Learn & practice AWS Hacking:

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{% endhint %} ## Basic Information As the name implies, this vulnerability occurs when a program **stores some space** in the heap for an object, **writes** some info there, **frees** it apparently because it's not needed anymore and then **accesses it again**. The problem here is that it's not ilegal (there **won't be errors**) when a **freed memory is accessed**. So, if the program (or the attacker) managed to **allocate the freed memory and store arbitrary data**, when the freed memory is accessed from the initial pointer that **data would be have been overwritten** causing a **vulnerability that will depends on the sensitivity of the data** that was stored original (if it was a pointer of a function that was going to be be called, an attacker could know control it). ### First Fit attack A first fit attack targets the way some memory allocators, like in glibc, manage freed memory. When you free a block of memory, it gets added to a list, and new memory requests pull from that list from the end. Attackers can use this behavior to manipulate **which memory blocks get reused, potentially gaining control over them**. This can lead to "use-after-free" issues, where an attacker could **change the contents of memory that gets reallocated**, creating a security risk.\ Check more info in: {% content-ref url="use-after-free/first-fit" %} [first-fit](https://angelica.gitbook.io/hacktricks/binary-exploitation/libc-heap/use-after-free/first-fit) {% endcontent-ref %} {% hint style="success" %} Learn & practice AWS Hacking:

[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)

\ Learn & practice GCP Hacking:

[**HackTricks Training GCP Red Team Expert (GRTE)**

](https://training.hacktricks.xyz/courses/grte)

Support HackTricks

{% endhint %}