Security

Security Review Guide

Comprehensive vulnerability taxonomy and review methodology for code security reviews. Project-specific security policies (CLAUDE.md, security docs) always take priority over this guidance.

Common Vulnerability Classes

Injection

• SQL injection: Unsanitized user input in queries; use parameterized queries or ORM query builders
• Command injection: User input passed to shell commands; avoid shell execution or use strict allowlists
• LDAP injection: Unsanitized input in LDAP queries
• Header injection: User input in HTTP headers enabling response splitting

Cross-Site Scripting (XSS)

• Reflected: User input echoed in responses without encoding
• Stored: Persistent user input rendered without encoding
• DOM-based: Client-side JavaScript manipulating DOM with unsanitized data

Cross-Site Request Forgery (CSRF)

• Missing or weak CSRF token validation
• Token not bound to user session
• GET requests performing state changes

Authentication Flaws

• Weak credential handling or storage
• Insecure session management
• Missing authentication checks on protected endpoints

Authorization Flaws

• Broken access control, privilege escalation
• Insecure Direct Object References (IDOR)
• Missing tenant isolation in multi-tenant systems

Cryptographic Issues

• Weak algorithms (MD5, SHA1 for security purposes)
• Improper key management or hardcoded secrets
• Insufficient entropy in token/nonce generation

Information Disclosure

• Sensitive data in logs, error messages, or API responses
• Stack traces or debug info exposed in production
• Credentials or tokens in URLs

Insecure Deserialization

• Unsafe parsing of untrusted data formats
• Object instantiation from user-controlled input

Domain-Specific Concerns

Race Conditions

• TOCTOU bugs: Time-of-check-to-time-of-use allowing business logic violations (double-spending, duplicate issuance)
• Concurrent access: Missing locking or optimistic concurrency control on shared resources

OAuth 2.0 Pitfalls

• Token leakage via referrer headers or logs
• Insufficient scope validation
• Redirect URI manipulation (open redirect, partial matching)
• Authorization code replay
• PKCE bypass or missing PKCE enforcement
• Refresh token rotation issues

OpenID Connect Pitfalls

• ID token validation gaps (signature, expiry, issuer, audience)
• Nonce misuse or missing nonce validation
• at_hash / c_hash verification omitted
• Issuer confusion in multi-provider setups

Session Security

• Session fixation or hijacking
• Insufficient expiration (idle and absolute timeouts)
• Cookie attribute misconfiguration (missing Secure, HttpOnly, SameSite)

Timing Attacks

• Non-constant-time comparisons on secrets, tokens, or hashes — all secret comparisons (passwords, tokens, HMAC digests, API keys) must use constant-time operations (e.g., ActiveSupport::SecurityUtils.secure_compare, hmac.compare_digest, crypto.timingSafeEqual)
• Observable timing differences in authentication flows (e.g., different response times for valid vs invalid usernames)
• Database lookups that short-circuit on missing records before performing credential verification

Review Methodology

1. Read the actual code — do not rely on summaries or assumptions; open and read every file under review and follow references to understand the full call chain
2. Analyze each change against the vulnerability classes above
3. Check surrounding code — vulnerabilities often arise from interactions between new and existing code
4. Verify both presence and absence — confirm mitigations exist where needed, and note areas reviewed that appeared secure

Severity Classification

• Critical: Remotely exploitable, no authentication required, leads to full system compromise or mass data breach
• High: Exploitable with low complexity, leads to significant data exposure or privilege escalation
• Medium: Requires specific conditions to exploit, limited blast radius
• Low: Minor issue, difficult to exploit, minimal impact
• Informational: Best practice deviation, defense-in-depth recommendation

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