Why Snyk Doesn’t Catch Fake Runtime Behavior

Snyk is excellent at finding vulnerable dependencies and security issues. But it cannot detect fake runtime behavior because mocks and stubs are not security vulnerabilities.

What Snyk catches

• Vulnerable dependencies
• Known security vulnerabilities
• License compliance issues
• Container image vulnerabilities
• IaC security misconfigurations

What Snyk misses

• Mock data serving real users
• Fallback clients returning fabricated responses
• Placeholder API endpoints in production
• Missing auth checks (not a vuln, just missing)
• Fake database connections

The gap

Snyk scans for known bad patterns. Mock data in production is a valid pattern applied incorrectly. A fallback client is not a vulnerability—it's a feature that's being used in the wrong context.

The solution: Add a reality gate

Complement Snyk with a deploy gate that validates:

• Runtime service wiring
• Endpoint contract enforcement
• Auth coverage verification
• Mock/stub detection

Practical example

# Snyk scan (existing) snyk test # Add reality gate (new) npx guardrail mockproof npx guardrail gate

Result

Snyk protects against known vulnerabilities. The reality gate protects against fake behavior. Together they secure both dependencies and runtime.

Some teams use guardrail to detect this automatically in CI.