Linux Heap glibc 2.27 Double Free Exploitation

In this paper, I introduce the reader to a heap metadata corruption against the glibc 2.27 Linux Heap Allocator, ptmalloc. This attack is mitigated in the most recent 2.29 glibc. An attacker that forces the application to perform a double free can manipulate it to make malloc return an arbitrary pointer. This is achieved, by having malloc return a chunk of memory whilst still remaining in the tcache freelist. The attacker is then able to manipulate this memory to perform tcache poisoning and force malloc to return an arbitrary pointer. This is a powerful primitive, and with appropriate application logic is equivalent of a write-what-where.

Linux Heap glibc 2.27 Double Free Exploitation.PDF

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