Static Application Security Testing (SAST): Writing Custom Semgrep Rules

Semantic code pattern matching, abstract syntax tree queries, eliminating false positives, and CI build gating.

1. Core Architectural Analysis

Modern production environments cannot rely on perimeter assumptions. When analyzing Static Application Security Testing (SAST): Writing Custom Semgrep Rules, systems engineers must evaluate the boundary conditions where software invariants meet low-level platform execution.

In high-assurance environments, security failures are rarely arbitrary. They arise from deterministic oversights in memory management, concurrency models, or protocol parsing hierarchies. Mitigating these systemic risks requires rigorous instrumentation and proactive architectural defense.

2. Practical Implementation & Verification

Consider the following implementation blueprint illustrating the critical design constraints:

rules:
  - id: hardcoded-secret-detection
    pattern: const $KEY = "..."
    message: "Detected potential hardcoded cryptographic token"
    languages: [typescript, javascript]
    severity: ERROR

3. Engineering Takeaways & Hardening Strategies

• Defense in Depth: Ensure every layer independently validates state transitions rather than assuming upstream sanitize guarantees.
• Continuous Telemetry: Instrument telemetry probes at the lowest feasible operating layer to capture anomalies in real time without performance degradation.
• Deterministic Verification: Complement runtime mitigations with compile-time type safety, automated fuzzing harnesses, and formal constraint checking.

Published as part of the Zero Day Diary engineering research archive by Veer Bhanushali.