API security testing: SAST, DAST, IAST, fuzzing

Method overview

• SAST: Inspects source or specs for missing auth, weak schemas, and unsafe defaults.
• DAST: Probes running services to find runtime issues like CORS misconfig or verbose errors.
• IAST: Instruments apps to trace data flow during tests.
• Fuzzing: Generates malformed inputs to uncover crashes and logic bugs.

When to use each

Start with SAST in CI to block design flaws. Add DAST on staging to validate headers, TLS, and error hygiene. Use IAST for complex microservices where data lineage matters. Run fuzzers against high-risk endpoints such as auth and file uploads.

Build a layered program

• Gate merges with static API scanning.
• Schedule dynamic scans weekly.
• Instrument critical services for IAST and keep findings tied to Git issues.
• Use fuzzing to stress auth flows and file parsers before peak traffic events.