401-403-bypass-techniques

1# SKILL: 401/403 Bypass Techniques — Expert Attack Playbook
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3> **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.
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5## 0. RELATED ROUTING
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7- [authbypass-authentication-flaws](../authbypass-authentication-flaws/SKILL.md) — broader auth bypass (login flaws, session handling)
8- [waf-bypass-techniques](../waf-bypass-techniques/SKILL.md) — when bypass is WAF-specific rather than access control
9- [http-host-header-attacks](../http-host-header-attacks/SKILL.md) — Host header manipulation for routing bypass
10- [request-smuggling](../request-smuggling/SKILL.md) — smuggle past access controls entirely
11- [http2-specific-attacks](../http2-specific-attacks/SKILL.md) — h2c smuggling to bypass proxy ACLs
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15## 1. PATH MANIPULATION BYPASSES
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17The core idea: the reverse proxy/WAF checks one path format, but the backend normalizes differently.
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19### 1.1 Trailing Slash / Missing Slash
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21```
22/admin      → 403
23/admin/     → 200  ✓ (trailing slash)
24/admin/.    → 200  ✓ (trailing dot)
25```
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27### 1.2 Case Sensitivity
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29```
30/admin      → 403
31/Admin      → 200  ✓
32/ADMIN      → 200  ✓
33/aDmIn      → 200  ✓
34```
35…