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.

Insecure Defaults