401-403-bypass-techniqueslisted

# SKILL: 401/403 Bypass Techniques — Expert Attack Playbook > **AI LOAD INSTRUCTION**: Comprehensive 401/403 forbidden bypass techniques. Covers path normalization tricks, HTTP method override, header-based bypasses (X-Original-URL, X-Forwarded-For), protocol version tricks, and combination attacks. Base models typically know 2-3 header bypasses but miss the full matrix of path manipulation variants and verb+path combos. ## 0. RELATED ROUTING - [authbypass-authentication-flaws](../authbypass-authentication-flaws/SKILL.md) — broader auth bypass (login flaws, session handling) - [waf-bypass-techniques](../waf-bypass-techniques/SKILL.md) — when bypass is WAF-specific rather than access control - [http-host-header-attacks](../http-host-header-attacks/SKILL.md) — Host header manipulation for routing bypass - [request-smuggling](../request-smuggling/SKILL.md) — smuggle past access controls entirely - [http2-specific-attacks](../http2-specific-attacks/SKILL.md) — h2c smuggling to bypass proxy ACLs --- ## 1. PATH MANIPULATION BYPASSES The core idea: the reverse proxy/WAF checks one path format, but the backend normalizes differently. ### 1.1 Trailing Slash / Missing Slash ``` /admin → 403 /admin/ → 200 ✓ (trailing slash) /admin/. → 200 ✓ (trailing dot) ``` ### 1.2 Case Sensitivity ``` /admin → 403 /Admin → 200 ✓ /ADMIN → 200 ✓ /aDmIn → 200 ✓ ``` Works when: proxy rule is case-sensitive but backend is case-insensitive (common on Windows/