trailofbits/insecure-defaults

Insecure Defaults Detection

Finds fail-open vulnerabilities where apps run insecurely with missing configuration. Distinguishes exploitable defaults from fail-secure patterns that crash safely.

• Fail-open (CRITICAL): SECRET = env.get('KEY') or 'default' → App runs with weak secret
• Fail-secure (SAFE): SECRET = env['KEY'] → App crashes if missing

When to Use

• Security audits of production applications (auth, crypto, API security)
• Configuration review of deployment files, IaC templates, Docker configs
• Code review of environment variable handling and secrets management
• Pre-deployment checks for hardcoded credentials or weak defaults

When NOT to Use

Do not use this skill for:

• Test fixtures explicitly scoped to test environments (files in test/, spec/, __tests__/)
• Example/template files (.example, .template, .sample suffixes)
• Development-only tools (local Docker Compose for dev, debug scripts)
• Documentation examples in README.md or docs/ directories
• Build-time configuration that gets replaced during deployment
• Crash-on-missing behavior where app won't start without proper config (fail-secure)

When in doubt: trace the code path to determine if the app runs with the default or crashes.

Rationalizations to Reject

• "It's just a development default" → If it reaches production code, it's a finding
• "The production config overrides it" → Verify prod config exists; code-level vulnerability remains if not
• "This would never run without proper config" → Prove it with code trace; many apps fail silently
• "It's behind authentication" → Defense in depth; compromised session still exploits weak defaults
• "We'll fix it before release" → Document now; "later" rarely comes

Workflow

Follow this workflow for every potential finding:

1. SEARCH: Perform Project Discovery and Find Insecure Defaults

Determine language, framework, and project conventions. Use this information to further discover things like secret storage locations, secret usage patterns, credentialed third-party integrations, cryptography, and any other relevant configuration. Further use information to analyze insecure default configurations.

Example Search for patterns in **/config/, **/auth/, **/database/, and env files:

• Fallback secrets: getenv.*\) or ['"], process\.env\.[A-Z_]+ \|\| ['"], ENV\.fetch.*default:
• Hardcoded credentials: password.*=.*['"][^'"]{8,}['"], api[_-]?key.*=.*['"][^'"]+['"]
• Weak defaults: DEBUG.*=.*true, AUTH.*=.*false, CORS.*=.*\*
• Crypto algorithms: MD5|SHA1|DES|RC4|ECB in security contexts

Tailor search approach based on discovery results.

Focus on production-reachable code, not test fixtures or example files.

2. VERIFY: Actual Behavior

For each match, trace the code path to understand runtime behavior.

Questions to answer:

• When is this code executed? (Startup vs. runtime)
• What happens if a configuration variable is missing?
• Is there validation that enforces secure configuration?

3. CONFIRM: Production Impact

Determine if this issue reaches production:

If production config provides the variable → Lower severity (but still a code-level vulnerability) If production config missing or uses default → CRITICAL

4. REPORT: with Evidence

Example report:

Finding: Hardcoded JWT Secret Fallback
Location: src/auth/jwt.ts:15
Pattern: const secret = process.env.JWT_SECRET || 'default';

Verification: App starts without JWT_SECRET; secret used in jwt.sign() at line 42
Production Impact: Dockerfile missing JWT_SECRET
Exploitation: Attacker forges JWTs using 'default', gains unauthorized access

Quick Verification Checklist

Fallback Secrets: SECRET = env.get(X) or Y → Verify: App starts without env var? Secret used in crypto/auth? → Skip: Test fixtures, example files

Default Credentials: Hardcoded username/password pairs → Verify: Active in deployed config? No runtime override? → Skip: Disabled accounts, documentation examples

Fail-Open Security: AUTH_REQUIRED = env.get(X, 'false') → Verify: Default is insecure (false/disabled/permissive)? → Safe: App crashes or default is secure (true/enabled/restricted)

Weak Crypto: MD5/SHA1/DES/RC4/ECB in security contexts → Verify: Used for passwords, encryption, or tokens? → Skip: Checksums, non-security hashing

Permissive Access: CORS *, permissions 0777, public-by-default → Verify: Default allows unauthorized access? → Skip: Explicitly configured permissiveness with justification

Debug Features: Stack traces, introspection, verbose errors → Verify: Enabled by default? Exposed in responses? → Skip: Logging-only, not user-facing

For detailed examples and counter-examples, see examples.md.