checking-session-security

What this skill does

# Checking Session Security

## Overview

Audit session management implementations in web applications to identify vulnerabilities including session fixation (CWE-384), insufficient session expiration (CWE-613), and cleartext transmission of session tokens (CWE-319).

## Prerequisites

- Application source code accessible in `${CLAUDE_SKILL_DIR}/`
- Session management code locations identified (auth modules, middleware, session stores)
- Framework and language identified (Express.js, Django, Spring Boot, Rails, ASP.NET, etc.)
- Session configuration files available (`session.config.*`, `settings.py`, `application.yml`)
- Write permissions for reports in `${CLAUDE_SKILL_DIR}/security-reports/`

## Instructions

1. Locate session management code by searching for patterns: `**/auth/**`, `**/session/**`, `**/middleware/**`, and framework-specific files (`settings.py`, `application.yml`, `web.config`).
2. **Analyze session ID generation**: verify use of a cryptographically secure random generator with at least 128 bits of entropy. Flag predictable patterns such as `Date.now()`, `Math.random()`, sequential IDs, or timestamp-based tokens (CWE-330).
3. **Check session fixation protections**: confirm the session ID is regenerated after authentication (`req.session.regenerate()` in Express, `request.session.cycle_key()` in Django). Flag any login handler that sets `authenticated = true` without regenerating the session ID.
4. **Validate cookie security attributes**: verify `HttpOnly` (prevents XSS-based token theft), `Secure` (HTTPS-only transmission), `SameSite=Lax|Strict` (CSRF mitigation), and `__Host-`/`__Secure-` prefix usage. Flag any missing attribute.
5. **Review session expiration**: check idle timeout (recommend 15-30 min for sensitive apps), absolute timeout (recommend 4-8 hours), and sliding window configuration. Flag sessions without any expiration.
6. **Audit session invalidation**: verify logout handlers destroy server-side session state and clear client cookies. Confirm password reset and privilege escalation flows invalidate existing sessions.
7. **Inspect session storage**: flag in-memory stores in production (no persistence across restarts), unencrypted session data at rest, and missing integrity checks on session payloads (e.g., unsigned JWT session tokens).
8. **Identify attack vectors**: assess exposure to session fixation, CSRF via session riding, replay attacks from stolen tokens, and session prediction from weak ID generation.
9. Produce the session security report at `${CLAUDE_SKILL_DIR}/security-reports/session-security-YYYYMMDD.md` with per-finding severity, CWE mapping, vulnerable code snippet, and remediated code example.

See `${CLAUDE_SKILL_DIR}/references/implementation.md` for the detailed implementation guide. See `${CLAUDE_SKILL_DIR}/references/critical-findings.md` for example vulnerability patterns with before/after code.

## Output

- **Session Security Report**: `${CLAUDE_SKILL_DIR}/security-reports/session-security-YYYYMMDD.md` with findings by severity
- **Cookie Attribute Matrix**: per-cookie compliance table (HttpOnly, Secure, SameSite, prefix)
- **Vulnerable Code Listings**: each finding with file path, line number, vulnerable snippet, and fix
- **Framework-Specific Remediation**: configuration changes tailored to the detected framework

## Error Handling

| Error | Cause | Solution |
|-------|-------|----------|
| No session handling code found in `${CLAUDE_SKILL_DIR}/` | Unusual file structure or framework | Search for framework-specific patterns; request explicit file paths |
| Unknown session framework | Custom or uncommon session library | Apply fundamental session security principles; note limited framework-specific guidance |
| Cannot analyze minified/compiled code | Production bundles instead of source | Request unminified source code; document limitation |
| Non-standard session implementation | Custom session management bypassing framework | Apply extra scrutiny; custom implementations are higher risk (CWE-384, CWE-613) |
| Session config in environment variables, not code | Externalized configuration | Request `.env.example` or deployment config documentation |

## Examples

- "Audit session cookie flags and rotation logic for fixation and CSRF risks in the Express.js application."
- "Review logout and password reset flows to confirm sessions are invalidated correctly and old tokens cannot be replayed."
- "Check session ID generation entropy and storage backend security for the Django application."

## Resources

- OWASP Session Management Cheat Sheet: https://cheatsheetseries.owasp.org/cheatsheets/Session_Management_Cheat_Sheet.html
- CWE-384 Session Fixation: https://cwe.mitre.org/data/definitions/384.html
- CWE-613 Insufficient Session Expiration: https://cwe.mitre.org/data/definitions/613.html
- CWE-319 Cleartext Transmission: https://cwe.mitre.org/data/definitions/319.html
- NIST 800-63B Digital Authentication: https://pages.nist.gov/800-63-3/sp800-63b.html
- `${CLAUDE_SKILL_DIR}/references/critical-findings.md` -- example vulnerability patterns
- `${CLAUDE_SKILL_DIR}/references/errors.md` -- full error handling reference
- https://intentsolutions.io