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Educational Heap Exploitation

This repo is for learning various heap exploitation techniques. We use Ubuntu's Libc releases as the gold-standard. Each technique is verified to work on corresponding Ubuntu releases. You can run apt source libc6 to download the source code of the Libc your are using on Debian-based operating system. You can also click ▶️ to debug the technique in your browser using gdb.

We came up with the idea during a hack meeting, and have implemented the following techniques:

File ▶️ Technique Glibc-Version Patch Applicable CTF Challenges
first_fit.c Demonstrating glibc malloc's first-fit behavior.
calc_tcache_idx.c Demonstrating glibc's tcache index calculation.
fastbin_dup.c ▶️ Tricking malloc into returning an already-allocated heap pointer by abusing the fastbin freelist. latest
fastbin_dup_into_stack.c ▶️ Tricking malloc into returning a nearly-arbitrary pointer by abusing the fastbin freelist. latest 9447-search-engine, 0ctf 2017-babyheap
fastbin_dup_consolidate.c ▶️ Tricking malloc into returning an already-allocated heap pointer by putting a pointer on both fastbin freelist and the top chunk. latest Hitcon 2016 SleepyHolder
unsafe_unlink.c ▶️ Exploiting free on a corrupted chunk to get arbitrary write. latest HITCON CTF 2014-stkof, Insomni'hack 2017-Wheel of Robots
house_of_spirit.c ▶️ Frees a fake fastbin chunk to get malloc to return a nearly-arbitrary pointer. latest hack.lu CTF 2014-OREO
poison_null_byte.c ▶️ Exploiting a single null byte overflow. latest PlaidCTF 2015-plaiddb, BalsnCTF 2019-PlainNote
house_of_lore.c ▶️ Tricking malloc into returning a nearly-arbitrary pointer by abusing the smallbin freelist. latest
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 < 2.29 patch hack.lu CTF 2015-bookstore, Nuit du Hack 2016-night-deamonic-heap
overlapping_chunks_2.c ▶️ Exploit the overwrite of an in use chunk size in order to make a new allocation overlap with an existing chunk < 2.29 patch
mmap_overlapping_chunks.c Exploit an in use mmap chunk in order to make a new allocation overlap with a current mmap chunk latest
house_of_force.c ▶️ Exploiting the Top Chunk (Wilderness) header in order to get malloc to return a nearly-arbitrary pointer < 2.29 patch Boston Key Party 2016-cookbook, BCTF 2016-bcloud
unsorted_bin_into_stack.c ▶️ Exploiting the overwrite of a freed chunk on unsorted bin freelist to return a nearly-arbitrary pointer. < 2.29 patch
unsorted_bin_attack.c ▶️ Exploiting the overwrite of a freed chunk on unsorted bin freelist to write a large value into arbitrary address < 2.29 patch 0ctf 2016-zerostorage
large_bin_attack.c ▶️ Exploiting the overwrite of a freed chunk on large bin freelist to write a large value into arbitrary address latest 0ctf 2018-heapstorm2
house_of_einherjar.c ▶️ Exploiting a single null byte overflow to trick malloc into returning a controlled pointer latest Seccon 2016-tinypad
house_of_water.c Exploit a UAF or double free to gain leakless control of the t-cache metadata and a leakless way to link libc in t-cache latest 37c3 Potluck - Tamagoyaki
sysmalloc_int_free.c Demonstrating freeing the nearly arbitrary sized Top Chunk (Wilderness) using malloc (sysmalloc _int_free() ) latest
house_of_orange.c ▶️ Exploiting the Top Chunk (Wilderness) in order to gain arbitrary code execution < 2.26 patch Hitcon 2016 houseoforange
house_of_tangerine.c Exploiting the Top Chunk (Wilderness) in order to trick malloc into returning a completely arbitrary pointer by abusing the tcache freelist >= 2.26 PicoCTF 2024- high frequency troubles
house_of_roman.c ▶️ Leakless technique in order to gain remote code execution via fake fastbins, the unsorted_bin attack and relative overwrites. < 2.29 patch
tcache_poisoning.c ▶️ Tricking malloc into returning a completely arbitrary pointer by abusing the tcache freelist. (requires heap leak on and after 2.32) > 2.25 patch
tcache_house_of_spirit.c ▶️ Frees a fake chunk to get malloc to return a nearly-arbitrary pointer. > 2.25
house_of_botcake.c ▶️ Bypass double free restriction on tcache. Make tcache_dup great again. > 2.25
tcache_stashing_unlink_attack.c ▶️ Exploiting the overwrite of a freed chunk on small bin freelist to trick malloc into returning an arbitrary pointer and write a large value into arbitraty address with the help of calloc. > 2.25 Hitcon 2019 one punch man
fastbin_reverse_into_tcache.c ▶️ Exploiting the overwrite of a freed chunk in the fastbin to write a large value into an arbitrary address. > 2.25
house_of_mind_fastbin.c ▶️ Exploiting a single byte overwrite with arena handling to write a large value (heap pointer) to an arbitrary address latest
house_of_storm.c ▶️ Exploiting a use after free on both a large and unsorted bin chunk to return an arbitrary chunk from malloc < 2.29
house_of_gods.c ▶️ A technique to hijack a thread's arena within 8 allocations < 2.27
decrypt_safe_linking.c ▶️ Decrypt the poisoned value in linked list to recover the actual pointer >= 2.32
safe_link_double_protect.c Leakless bypass for PROTECT_PTR by protecting a pointer twice, allowing for arbitrary pointer linking in t-cache >= 2.32 37c3 Potluck - Tamagoyaki
tcache_dup.c(obsolete) Tricking malloc into returning an already-allocated heap pointer by abusing the tcache freelist. 2.26 - 2.28 patch

The GnuLibc is under constant development and several of the techniques above have let to consistency checks introduced in the malloc/free logic. Consequently, these checks regularly break some of the techniques and require adjustments to bypass them (if possible). We address this issue by keeping multiple versions of the same technique for each Glibc-release that required an adjustment. The structure is glibc_<version>/technique.c.

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.

Get Started

Quick Setup

  • make sure you have the following packages/tools installed: patchelf zstd wget (of course also build-essential or similar for compilers, make, ...)
  • also, /usr/bin/python must be/point to your python binary (e. g. /usr/bin/python3)
git clone https://github.com/shellphish/how2heap
cd how2heap
make clean base
./malloc_playground

Notice that this will link the binaries with your system libc. If you want to play with other libc versions. Please refer to Complete Setup.

Complete Setup

You will encounter symbol versioning issues (see this) if you try to LD_PRELOAD libcs to a binary that's compiled on your host machine. We have two ways to bypass it.

Method 1: link against older libc

This one tells linker to link the target binary with the target libc.

git clone https://github.com/shellphish/how2heap
cd how2heap
H2H_USE_SYSTEM_LIBC=N make v2.23

This will link all the binaries against corresponding libcs. What's better is that it comes with debug symbols. Now you can play with any libc versions on your host machine. In this example, it will compile all glibc-2.23 binaries and link them with libc-2.23. You can change the number to play with other libc versions.

Method 2: use docker

This uses Docker-based approach to complie binaries inside an old ubuntu container so it is runnable with the target libc version.

git clone https://github.com/shellphish/how2heap
cd how2heap

# the next command will prepare the target binary so it runs with
# the expected libc version
make base
./glibc_run.sh 2.30 ./malloc_playground -d -p

# now you can play with the binary with glibc-2.30
# and even debug it with the correct symbols
readelf -d -W malloc_playground | grep RUNPATH # or use checksec
readelf -l -W malloc_playground | grep interpreter
gdb -q -ex "start" ./malloc_playground

Heap Exploitation Tools

There are some heap exploitation tools floating around.

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.

Pwngdb

Examine the glibc heap in gdb: https://github.com/scwuaptx/Pwngdb

pwndbg

An exploitation-centric gdb plugin that provides the ability to view/tamper with the glibc heap: https://github.com/pwndbg/pwndbg

gef

Another excellent gdb plugin that provides the ability to examine the glibc heap: https://github.com/hugsy/gef

heap-viewer

Examine the glibc heap in IDA Pro: https://github.com/danigargu/heap-viewer

Forkever

Debugger that lets you set "checkpoints" as well as view and edit the heap using a hexeditor: https://github.com/haxkor/forkever

heaptrace

Helps you visualize heap operations by replacing addresses with symbols: https://github.com/Arinerron/heaptrace

Other resources

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

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.