Getting it into your agent
It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.
git clone --depth 1 https://github.com/SecurityTalent/bugskill-ainpx agentmods add skills/securitytalent/bugskill-ai/401-403-bypass-techniquesWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/securitytalent/bugskill-ai/401-403-bypass-techniques)<a href="https://agentmods.dev/skills/securitytalent/bugskill-ai/401-403-bypass-techniques"><img src="https://agentmods.dev/badge/skills/securitytalent/bugskill-ai/401-403-bypass-techniques/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/securitytalent/bugskill-ai/401-403-bypass-techniques"><img src="https://agentmods.dev/badge/skills/securitytalent/bugskill-ai/401-403-bypass-techniques.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00053 | $0.03169 |
| Opus 5.5 | $0.00021 | $0.01268 |
| Sonnet 5.5 | $0.00011 | $0.00634 |
| Haiku 4.5 | $0.00005 | $0.00317 |
Grade A, and why
401-403-bypass-techniques scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
This is a copy
100% identical to 401-403-bypass-techniques — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 349 lines — stays where its author put it; the contents beside it link to each section on GitHub.
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 — broader auth bypass (login flaws, session handling)
- waf-bypass-techniques — when bypass is WAF-specific rather than access control
- http-host-header-attacks — Host header manipulation for routing bypass
- request-smuggling — smuggle past access controls entirely
- http2-specific-attacks — 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/IIS).
1.3 URL Encoding
/admin → 403
/%61dmin → 200 ✓ (encode 'a')
/admi%6e → 200 ✓ (encode 'n')
/%61%64%6d%69%6e → 200 ✓ (full encode)
1.4 Double URL Encoding
/admin → 403
/%2561dmin → 200 ✓ (%25 = %, decoded twice: %61 → a)
/admin%252f → 200 ✓
/admin..%252f → 200 ✓
1.5 Unicode / UTF-8 Encoding
/admin → 403
/admi%C0%AE → 200 ✓ (overlong UTF-8 for '.')
/admi%C0%6E → 200 ✓ (overlong encoding)
/%C0%AFadmin → 200 ✓ (overlong '/')
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 349 lines · 53 tokens per session scan A 71212134e73c
401-403-bypass-techniques is a skill published in the GitHub repository SecurityTalent/bugskill-ai (13 stars, last pushed 21d ago), licensed MIT. It adds 53 tokens to every session and 3,169 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 100% identical to 401-403-bypass-techniques, differing in 0 lines, and is treated as a copy.
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