ECFuzz

Evolutionary Coverage-guided Fuzzing engine. Requires clang 14 and llvm tools.

Quick Start

There are 2 errors in fuzz_target.c, occurring after some 'if' statements depending on user input. The program will compile and run the target file with embedded instrumentation, and send mutated inputs based on the samples in ./input/corpus to the executable's standard input. The code coverage of each new input is monitored, and any inputs yielding new code coverage will be added to the corpus.

bash cargo install ecfuzz git clone https://github.com/matt24smith/ecfuzz.git && cd ecfuzz export CFLAGS="-std=c17 -g -fcolor-diagnostics -O3" ecfuzz --target fuzz_target.c --corpus ./input/corpus --dictionary-path input/sample.dict --seed 000 --iterations 5000

Initializing the fuzzing engine with seed 000 finds both bugs in fuzz_target.c after ~4700 attempts. Results will be deterministic as long as the corpus, dictionary, and seed remain unchanged. Mutations will be logged to the same directory as the corpus file.

```text ... branch hits: 10/12 exec/s: 63.21 inputs: 2 i: 4600 ABCDE0001000000 crashing path A... fuzztarget.c:12:15: runtime error: applying zero offset to null pointer
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior fuzztarget.c:12:15 in fuzztarget.c:12:15: runtime error: store to null pointer of type 'char' SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior fuzztarget.c:12:15 in

This frame has 1 object(s): [32, 288) 'str1' <== Memory access at offset 32 is inside this variable

SUMMARY: AddressSanitizer: unknown-crash (/home/matt/ecfuzz/a.out+0x11a322) (BuildId: d47f3011239226931362fe3a8999c8bc129a9a52) in do_comparison Shadow bytes around the buggy address: 0x10005a40c570: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10005a40c580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =>0x10005a40c590: f1 f1 f1 f1[00]00 00 00 00 00 00 00 00 00 00 00 0x10005a40c5a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10005a40c5b0: 00 00 00 00 f3 f3 f3 f3 f3 f3 f3 f3 00 00 00 00 Shadow byte legend (one shadow byte represents 8 application bytes): Addressable: 00 Stack left redzone: f1 Stack mid redzone: f2 Stack right redzone: f3 ... crashing input: ABCDEF000000000 ```

See the full list of options with the --help flag

bash ecfuzz --help

Another example shows implementation of a custom fuzzer for examples/example_lib.c and examples/example.c, sending inputs as arguments to the target executable bash cargo run --example=example_custom_fuzzer

Windows users can download clang+LLVM here: https://github.com/llvm/llvm-project/releases/download/llvmorg-14.0.6/LLVM-14.0.6-win64.exe

Distillation Strategy

1. compile target with code coverage mapping, asan, and usan
2. mutate one of the seeded inputs, and send it to the target via stdin
3. measure code coverage as a set of code branches executed
4. if a new branch is discovered by a mutation, add it to the corpus.
   • 4b. compare the new branch coverage to existing corpus entries, and prune entries with a coverage subset of the newest coverage

Mutations

• XOR bit flip + byteshift
• byte replacement
• magic character replacement
• dictionary insertion
• tokenized dictionary replacement

Try it out! bash ecfuzz --help | tail -n+4 | ecfuzz --mutate-stdin --seed 1

Dictionary mutations

To enable dictionary mutations, a dictionary filepath must be included. Lines in the dictionary file containing key items will be spliced into the input. Dictionary lines containing key=value will be inserted using tokenized replacement , e.g. mutate a key item in the seed input by replacing it with a value. Keys are split on the first = symbol, and keys may be repeated on a new line for multiple values.