SAST vs IAST: What's the Difference?

Overview

SAST (Static Application Security Testing) and IAST (Interactive Application Security Testing) both find application security vulnerabilities, but they work in fundamentally different ways. SAST analyzes code without running it. IAST instruments the running application and observes behavior during test execution.

How SAST Works

SAST tools analyze source code, bytecode, or binaries to find vulnerabilities by tracing data flows from user-controlled sources to dangerous sinks. SAST runs before the application executes — in CI, as a pre-commit hook, or on a scheduled basis. It can analyze 100% of code paths, including code that tests do not cover.

How IAST Works

IAST deploys an agent (typically a JVM agent, a Node.js hook, or a .NET profiler) into the running application. During test execution, the agent monitors all data flows in real time — tracking tainted data as it moves through the application. When tainted data reaches a dangerous operation during an actual execution, IAST reports a confirmed finding.

Because IAST observes actual execution, its findings are confirmed by real data flows — dramatically reducing false positives compared to SAST.

Trade-offs

The IAST advantage (lower false positives) comes at costs: IAST requires deploying an agent, only analyzes code exercised during testing, and cannot run in pre-commit or early CI stages. SAST has higher false positives but provides immediate feedback on all code, including untested paths.

Connection to Autonomous Code Governance

IAST's confirmed findings are ideal inputs for autonomous remediation: low false positive rates mean that autonomous action on IAST findings is less likely to waste engineering review time. Hydra can ingest IAST findings alongside SAST findings, applying its remediation pipeline to the higher-confidence IAST results with greater confidence and lower human oversight requirements.