AddressSanitizer
Runs C, C++ and Rust code under AddressSanitizer to catch memory errors.
Install
npx skills add trailofbits/skills --skill address-sanitizer -g -a claude-code -y- Repository
- trailofbits/skills7.9k
- Category
- Security
- Updated
- 7d ago
- License
- CC-BY-SA-4.0
- Context cost
- Mediumabout 2,768 tokens
- Runs scripts
- No, instructions only
What it does
Builds and runs code under AddressSanitizer to catch buffer overflows, use-after-free, and other memory errors during fuzzing or tests. Covers -fsanitize=address builds, ASAN_OPTIONS, reading the crash report, LeakSanitizer, and the overhead and platform trade-offs. Use when fuzzing C/C++ or Rust that has unsafe blocks or FFI, when debugging a memory corruption crash, or when reading an ASan stack trace.
AddressSanitizer (ASan)
AddressSanitizer (ASan) is a widely adopted memory error detection tool used extensively during software testing, particularly fuzzing. It helps detect memory corruption bugs that might otherwise go unnoticed, such as buffer overflows, use-after-free errors, and other memory safety violations.
Overview
ASan is a standard practice in fuzzing due to its effectiveness in identifying memory vulnerabilities. It instruments code at compile time to track memory allocations and accesses, detecting illegal operations at runtime.
Key Concepts
| Concept | Description |
|---|---|
| Instrumentation | ASan adds runtime checks to memory operations during compilation |
| Shadow Memory | Maps 20TB of virtual memory to track allocation state |
| Performance Cost | Approximately 2-4x slowdown compared to non-instrumented code |
| Detection Scope | Finds buffer overflows, use-after-free, double-free, and memory leaks |
When to Apply
Apply this technique when:
- Fuzzing C/C++ code for memory safety vulnerabilities
- Testing Rust code with unsafe blocks
- Debugging crashes related to memory corruption
- Running unit tests where memory errors are suspected
Skip this technique when:
- Running production code (ASan can reduce security)
- Platform is Windows or macOS (limited ASan support)
- Performance overhead is unacceptable for your use case
- Fuzzing pure safe languages without FFI (e.g., pure Go, pure Java)
Quick Reference
| Task | Command/Pattern |
|---|---|
| Enable ASan (Clang/GCC) | -fsanitize=address |
| Enable verbosity | ASAN_OPTIONS=verbosity=1 |
| Disable leak detection | ASAN_OPTIONS=detect_leaks=0 |
| Force abort on error | ASAN_OPTIONS=abort_on_error=1 |
| Multiple options | ASAN_OPTIONS=verbosity=1:abort_on_error=1 |
Step-by-Step
Step 1: Compile with ASan
Compile and link your code with the -fsanitize=address flag:
