Performing Fuzzing With Aflplusplus

Performing Fuzzing with AFL++

Overview

AFL++ is a community-maintained fork of American Fuzzy Lop (AFL) that provides coverage-guided fuzzing for compiled binaries. It instruments targets at compile time or via QEMU/Unicorn mode for binary-only fuzzing, then mutates input corpora to discover new code paths. AFL++ includes advanced scheduling (MOpt, rare), custom mutators, CMPLOG for input-to-state comparison solving, and persistent mode for high-throughput fuzzing.

When to Use

Trigger phrases:

• "performing fuzzing with aflplusplus"

• "Perform coverage-guided fuzzing of compiled binaries using AFL++ (American Fuzzy"

• When conducting security assessments that involve performing fuzzing with aflplusplus

• When following incident response procedures for related security events

• When performing scheduled security testing or auditing activities

• When validating security controls through hands-on testing

Prerequisites

• AFL++ installed (apt install afl++ or build from source)
• Target binary source code (for compile-time instrumentation) or QEMU mode for binary-only
• Initial seed corpus of valid inputs for the target format
• Linux system with /proc/sys/kernel/core_pattern configured

Steps

1. Instrument the target binary with afl-cc or afl-clang-fast
2. Prepare seed corpus directory with minimal valid inputs
3. Minimize corpus with afl-cmin to remove redundant seeds
4. Run afl-fuzz with appropriate flags (-i input -o output)
5. Monitor fuzzing progress via afl-whatsup and UI stats
6. Triage crashes with afl-tmin minimization and CASR/GDB analysis
7. Report unique crashes with reproduction steps

Expected Output

+++ Findings +++
  unique crashes: 12
  unique hangs: 3
  last crash: 00:02:15 ago
+++ Coverage +++
  map density: 4.23% / 8.41%
  paths found: 1847
  exec speed: 2145/sec

When NOT to Use

• You don't have explicit written authorization to test
• Task is about defense/detection, not offense (use detection skills)
• You need to implement security controls (use implementing-* skills)
• Task requires compliance auditing (use auditing-* skills)
• You're investigating an incident (use incident response skills)
• Target is out of scope for your engagement
• Task is about vulnerability scanning only (use scanning tools)

Red Flags

• Performing actions without explicit written authorization from the asset owner
• Testing against production systems without a defined scope and rules of engagement
• Sharing sensitive findings or credentials in unencrypted communications
• Failing to properly scope and contain the assessment before starting

Process

1. Design — Define interface, identify patterns, plan implementation
2. Implement — Write code following existing conventions, add tests
3. Verify — Run tests, check integration, validate behavior

Verification

• All steps executed successfully against a test environment before production use
• Output documented with screenshots or logs demonstrating expected behavior
• Results validated against known-good baselines or reference implementations
• Documentation complete enough for another analyst to reproduce findings

Anti-Rationalization Table