thehepta / how2heap

A repository for learning various heap exploitation techniques.

Educational Heap Exploitation

This repo is for learning various heap exploitation techniques. We came up with the idea during a hack meeting, and have implemented the following techniques:

File	Technique	Applicable CTF Challenges
first_fit.c	Demonstrating glibc malloc's first-fit behavior.
fastbin_dup.c	Tricking malloc into returning an already-allocated heap pointer by abusing the fastbin freelist.
fastbin_dup_into_stack.c	Tricking malloc into returning a nearly-arbitrary pointer by abusing the fastbin freelist.	9447-search-engine
unsafe_unlink.c	Exploiting free on a corrupted chunk to get arbitrary write.	HITCON CTF 2014-stkof
house_of_spirit.c	Frees a fake fastbin chunk to get malloc to return a nearly-arbitrary pointer.	hack.lu CTF 2014-OREO
poison_null_byte.c	Exploiting a single null byte overflow.	PlaidCTF 2015-plaiddb
house_of_lore.c	Tricking malloc into returning a nearly-arbitrary pointer by abusing the smallbin freelist.
overlapping_chunks.c	Exploit the overwrite of a freed chunk size in the unsorted bin in order to make a new allocation overlap with an existing chunk	hack.lu CTF 2015-bookstore
house_of_force.c	Exploiting the Top Chunk (Wilderness) header in order to get malloc to return a nearly-arbitrary pointer	Boston Key Party 2016-cookbook, BCTF 2016-bcloud
unsorted_bin_attack.c	Exploiting the overwrite of a freed chunk on unsorted bin freelist to write a large value into arbitrary address	0ctf 2016-zerostorage

Have a good example? Add it here! Try to inline the whole technique in a single .c -- it's a lot easier to learn that way.

Heap Exploitation Tools

There are some heap exploitation tools floating around.

libheap

Examine the glibc heap in gdb: https://github.com/cloudburst/libheap

Malloc Playground

The malloc_playground.c file given is the source for a program that prompts the user for commands to allocate and free memory interactively.

Other resources

Some good heap exploitation resources, roughly in order of their publication, are:

• ptmalloc fanzine, a set of resources and examples related to meta-data attacks on ptmalloc: http://tukan.farm/2016/07/26/ptmalloc-fanzine/
• A malloc diagram, from libheap: https://raw.githubusercontent.com/cloudburst/libheap/master/heap.png
• Glibc Adventures: The Forgotten Chunk (http://www.contextis.com/documents/120/Glibc_Adventures-The_Forgotten_Chunks.pdf) - advanced heap exploitation
• Pseudomonarchia jemallocum (http://www.phrack.org/issues/68/10.html)
• The House Of Lore: Reloaded (http://phrack.org/issues/67/8.html)
• Malloc Des-Maleficarum (http://phrack.org/issues/66/10.html) - some malloc exploitation techniques
• Yet another free() exploitation technique (http://phrack.org/issues/66/6.html)
• Understanding the heap by breaking it (https://www.blackhat.com/presentations/bh-usa-07/Ferguson/Whitepaper/bh-usa-07-ferguson-WP.pdf) - explains heap implementation and a couple exploits
• The use of set_head to defeat the wilderness (http://phrack.org/issues/64/9.html)
• The Malloc Maleficarum (http://seclists.org/bugtraq/2005/Oct/118)
• OS X heap exploitation techniques (http://phrack.org/issues/63/5.html)
• Exploiting The Wilderness (http://seclists.org/vuln-dev/2004/Feb/25)
• Advanced Doug lea's malloc exploits (http://phrack.org/issues/61/6.html)

Hardening

There are a couple of "hardening" measures embedded in glibc, like export MALLOC_CHECK_=1 (enables some checks), export MALLOC_PERTURB_=1 (data is overwritten), export MALLOC_MMAP_THRESHOLD_=1 (always use mmap()), ...

More info: mcheck(), mallopt().

There's also some tracing support as mtrace(), malloc_stats(), malloc_info(), memusage, and in other functions in this family.