ECFuzz

Evolutionary Coverage-guided Fuzzing engine. Lightweight, multithreaded, fully deterministic. Corpus mutations are managed by a genetic algorithm selecting for maximized code coverage, filtering redundant inputs. A library interface is also provided in addition to the command-line utility. Requires clang 14 (or newer) and llvm tools.

Quick Start

Install clang and llvm tools with your preferred package manager. Alternatively, download an installer for clang+LLVM or build from source: https://github.com/llvm/llvm-project/releases/

Install ecfuzz with cargo, and run it using the command line interface. Setting the --mutate-stdin flag generates a single mutation from standard input without measuring code coverage. Mutated results are output to stdout.

cargo install ecfuzz
ecfuzz --help
ecfuzz --help | tail -n+4 | ecfuzz --mutate-stdin --seed 1

See examples below for a demonstration of how source code coverage is measured for a preset number of mutations.

How it works

Corpus Distillation

1. compile target with code coverage mapping and sanitizers
2. mutate one of the seeded inputs, and send it to the target via stdin, input file, or command args
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
   • compare the new branch coverage to existing corpus entries, and prune entries with a coverage subset of the newest coverage

Number Generation

The xxhash algorithm is used for number generation, which means that fuzzing results will be fully deterministic as long as the input remains unchanged, even across different platforms.

Mutations

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

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.

Examples

CLI

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 ./examples/cli/input/corpus to the executable. The code coverage of each new input is monitored, and any inputs yielding new code coverage will be added to the corpus.

git clone https://github.com/matt24smith/ecfuzz.git && cd ecfuzz

# set additional flags for the clang compiler 
export CFLAGS="-std=c17 -g -fcolor-diagnostics -O3"

# see 'ecfuzz --help' for a complete description of arguments
ecfuzz \
    --target ./examples/cli/fuzz_target.c \
    --corpus ./examples/cli/input/corpus \
    --dictionary-path ./examples/cli/input/sample.dict \
    --seed 0001 \
    --iterations 5000

Initializing the fuzzing engine with seed 0001 finds both bugs in fuzz_target.c after 4705 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.

...
branch hits: 10/12  exec/s: 63.21  inputs: 2  i: 4600  ABCDE0001000000
fuzz_target.c:12:15: runtime error: applying zero offset to null pointer       
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior fuzz_target.c:12:15 in 
fuzz_target.c:12:15: runtime error: store to null pointer of type 'char'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior fuzz_target.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 path A...
New crash! execs: 4628  crash log:
  Corpus { inputs: [
    CorpusInput:  { stem: "corpus", coverage: {}, lifetime: 7, preview: "ABCDEF\r00000000\r" }],
  Total coverage: {} }

Custom Fuzzer using ECFuzz Library

Another example shows implementation of a custom fuzzer for ./examples/lib_custom_fuzzer/example_lib.c and examples/lib_custom_fuzzer/example.c, sending inputs as arguments to the target executable

cargo run --example=custom_fuzzer