Heap Exploitation

The glibc library provides functions such as free and malloc to help developers manage the heap memory according to their use cases. It is the responsibility of the developer to:

  • free any memory he/she has obtained using malloc.
  • Do not free the same memory more than once.
  • Ensure that memory usage does not go beyond the amount of memory requested, in other terms, prevent heap overflows.

Failing to do makes the software vulnerable to various kinds of attacks. Shellphish, a famous Capture the Flag team from UC Santa Barbara, has done a great job in listing a variety of heap exploitation techniques in how2heap. Attacks described in "The Malloc Maleficarum" by "Phantasmal Phantasmagoria" in an email to the "Bugtraq" mailing list are also described.

A summary of the attacks has been described below:

Attack Target Technique
First Fit This is not an attack, it just demonstrates the nature of glibc's allocator ---
Double Free Making malloc return an already allocated fastchunk Disrupt the fastbin by freeing a chunk twice
Forging chunks Making malloc return a nearly arbitrary pointer Disrupting fastbin link structure
Unlink Exploit Getting (nearly)arbitrary write access Freeing a corrupted chunk and exploiting unlink
Shrinking Free Chunks Making malloc return a chunk overlapping with an already allocated chunk Corrupting a free chunk by decreasing its size
House of Spirit Making malloc return a nearly arbitrary pointer Forcing freeing of a crafted fake chunk
House of Lore Making malloc return a nearly arbitrary pointer Disrupting smallbin link structure
House of Force Making malloc return a nearly arbitrary pointer Overflowing into top chunk's header
House of Einherjar Making malloc return a nearly arbitrary pointer Overflowing a single byte into the next chunk

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