Fuzz testing in Chromium

go/chrome-fuzzing

Fuzzing is a testing technique that feeds auto-generated inputs to a piece of target code in an attempt to crash the code. It's one of the most effective methods we have for finding security and stability issues (see go/fuzzing-success). You can learn more about the benefits of fuzzing at go/why-fuzz.

This documentation covers the in-process guided fuzzing approach employed by different fuzzing engines, such as libFuzzer or [AFL]. To learn more about out-of-process fuzzers, please refer to the Blackbox fuzzing page in the ClusterFuzz documentation.

[TOC]

Getting Started

In Chromium, you can easily create and submit fuzz targets. The targets are automatically discovered by buildbots, built with different fuzzing engines, then uploaded to the distributed ClusterFuzz fuzzing system to run at scale.

You should fuzz any code which absorbs inputs from untrusted sources, such as the web. If the code parses, decodes, or otherwise manipulates that input, it's an especially good idea to fuzz it.

Create your first fuzz target and submit it by stepping through our Getting Started Guide.

Advanced Topics

• Using libfuzzer instead of FuzzTest.

• Improving fuzz target efficiency.

• Creating a fuzz target that expects a protobuf instead of a byte stream as input.

  *** note Note: You can also fuzz code that needs multiple mutated inputs, or to generate inputs defined by a grammar.

  ---

• Reproducing bugs found by libFuzzer/AFL and reported by ClusterFuzz.

• Fuzzing mojo interfaces using automatically generated libprotobuf-mutator fuzzers.

Further Reading

• LibFuzzer integration with Chromium and ClusterFuzz.
• Detailed references for other integration parts.
• Writing fuzzers for the non-browser parts of Chrome OS.
• Fuzzing browsertests if you need to fuzz multiple Chrome subsystems.

Trophies

• Issues automatically filed by ClusterFuzz.
• Issues filed manually after running fuzz targets.
• Bugs found in PDFium by manual fuzzing.
• Bugs found in open-source projects with libFuzzer.

Other Links

• Guided in-process fuzzing of Chrome components blog post.
• ClusterFuzz Stats for fuzz targets built with AddressSanitizer and
• http://go/chrome-fuzzing-dashboard Code covered by fuzz tests.