Static Application Security Testing with Semgrep

Static Application Security Testing analyses source code without running it, searching for patterns that indicate vulnerabilities. Because it reads the code directly, SAST can be run early and often, even before the application is deployable, and it points to the exact file and line of a problem. This makes it a natural fit for developer workflows and continuous integration, catching issues as they are written.

Analogy🏏Cricket

🍳 Think of it like cooking: A recipe can look flawless on paper, but a head chef only truly judges the dish by tasting the finished plate, because heat, timing, and the actual oven reveal problems the written method never shows. Just as tasting the cooked result catches what reading the recipe cannot, DAST probes the running application and catches the misconfigurations and runtime behaviour that reading the source cannot. This reveals DAST's stance: it judges the dish as it is actually served, not the recipe as it was merely written.

This lesson uses Semgrep, a popular open-source SAST tool, to make the concepts concrete. Semgrep matches code against rules written in a syntax that mirrors the code itself, which makes rules readable and easy to customise. Understanding how SAST sees code, its strengths in coverage and its weakness in false positives, lets you use it effectively rather than drowning in noise.

Analogy🏏Cricket

💰 Think of it like finance: A real audit that actually attempts a sample transaction proves beyond doubt whether a control can be bypassed, with little room for a false alarm, but it can only test the accounts and processes the auditors actually reach. Just as a hands-on audit yields high-confidence, low-false-positive results yet is bounded by what it examines, DAST yields high-confidence findings about real exploitability yet is bounded by the surface it can reach. This reveals its trade-off: what it confirms is solid, but it only confirms what it manages to touch.