ctf-web

ctf-web is a skill for Claude Code from ljagiello/ctf-skills. It costs 124 tokens per session (2,674 once invoked), scanned B, original, MIT.

A routing and reference guide for web-focused capture-the-flag security puzzles. It covers websites, APIs, browser code, login systems, file uploads, templates, and smart-contract interfaces.

In plain words
What is it for?
Mapping web targets and testing issues such as cross-site scripting, SQL injection, server-side request forgery, XML attacks, token flaws, authentication bypasses, and request smuggling.
Why use it?
It helps identify the application's trust boundaries and choose an appropriate way to investigate common web vulnerabilities.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter. Also seen: mentions Claude Code.

Good fit Mapping web targets and testing issues such as cross-site scripting, SQL injection, server-side request forgery, XML attacks, token flaws, authentication bypasses, and request smuggling.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/ljagiello/ctf-skills/ctf-web
About the project

ctf-skills is a collection of agent instructions for solving capture-the-flag security challenges, including web exploitation, binary vulnerabilities, cryptography, reverse engineering, forensics, and OSINT. It is intended for agents and people working through CTF problems, and its skills can be loaded into supported coding-agent workflows.

ljagiello/ctf-skills · 3,234 stars · on GitHub · ljagiello.github.io

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.

Any agent
npx skills add ljagiello/ctf-skills --skill ctf-web
Clone the repo
git clone --depth 1 https://github.com/ljagiello/ctf-skills

Made for: Claude Code.

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.

agentmods badge for ctf-web

README.md
[![agentmods](https://agentmods.dev/badge/skills/ljagiello/ctf-skills/ctf-web/github.svg)](https://agentmods.dev/skills/ljagiello/ctf-skills/ctf-web)
Your own site
<a href="https://agentmods.dev/skills/ljagiello/ctf-skills/ctf-web"><img src="https://agentmods.dev/badge/skills/ljagiello/ctf-skills/ctf-web/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.

agentmods 80×15 button for ctf-web

Your own site · 80×15
<a href="https://agentmods.dev/skills/ljagiello/ctf-skills/ctf-web"><img src="https://agentmods.dev/badge/skills/ljagiello/ctf-skills/ctf-web.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 124 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,674 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 2 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • Socket warn 17 Apr 2026
  • Snyk fail 17 Apr 2026
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 3 findings, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high YARA Match · line 88
    YARA rule matched a hack tool or exploit indicator (offensive tools, reconnaissance, privilege escalation, or exploit frameworks).
    Fix: Remove offensive tool references and exploit code. Legitimate agent skills should not contain penetration testing tools, exploit frameworks, or reconnaissance utilities.
  • medium Excessive Agency · line 90
    Skill enables autonomous high-impact decisions without human-in-the-loop verification. Critical operations (destructive commands, financial transactions, data deletion) should require explicit user confirmation.
    Fix: Add human-in-the-loop confirmation for destructive, irreversible, or high-impact operations. Never auto-execute commands that modify files, send data, or alter system state.
  • medium Data Exfiltration · line 98
    Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.
    Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
How audits are shown
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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00124 $0.02674
Opus 5 $0.00062 $0.01337
Sonnet 5 $0.00025 $0.00535
Haiku 4.5 $0.00012 $0.00267

Measured 11d ago against content hash 3fd4cafdb39b, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade B, and why

ctf-web scanned grade B with 2 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 11d 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.

Sends data to an external URLmediumData exfiltration

A POST to an outside endpoint may be telemetry or may be exfiltration; either way the mod talks to somewhere, and you should know where.

curl -v -X POST https://target.com/api -H "Content-Type: application/json" -d '{}'

Makes network callslowCapability

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

apt install hashcat jq curl
Origin

Copies of this mod

2 near-identical copies found in the catalogue:

ctf-web/SKILL.md · 153 lines

How it starts

The opening of the file, as written. The whole thing — 153 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CTF Web Exploitation

Use this skill as a routing and execution guide for web-heavy challenges. Keep the first pass short: map the app, confirm the trust boundary, and only then dive into the detailed technique notes.

Prerequisites

Python packages (all platforms):

pip install sqlmap flask-unsign requests

Linux (apt):

apt install hashcat jq curl

macOS (Homebrew):

brew install hashcat jq curl

Go tools (all platforms, requires Go):

go install github.com/ffuf/ffuf/v2@latest

Manual install:

  • ysoserial — GitHub, requires Java (Java deserialization payloads)

Additional Resources

  • sql-injection.md - SQL injection techniques: auth bypass, UNION extraction, filter bypasses, second-order SQLi, truncation, race-assisted leaks, INSERT ON DUPLICATE KEY UPDATE password overwrite, innodb_table_stats WAF bypass
  • server-side.md - PHP type juggling, php://filter LFI, Python str.format traversal, SSTI (Jinja2, Twig, ERB, Mako, EJS, Vue.js, Smarty), SSRF (Host header, DNS rebinding, curl redirect, unescaped-dot regex, SNI FTP smuggling, mod_vhost_alias), PHP hash_hmac NULL
  • server-side-2.md - XXE (basic, OOB, DOCX upload), XML injection via X-Forwarded-For, PHP variable variables, PHP uniqid predictable filename, sequential regex replacement bypass, command injection (newline, blocklist, sendmail CGI, multi-barcode, git CLI), GraphQL injection (introspection, batching, interpolation)
  • server-side-exec.md - Direct code execution paths, upload-to-RCE, deserialization-adjacent execution, LaTeX injection, header and API abuses
  • server-side-exec-2.md - More execution chains: SQLi fragmentation, path parser tricks, polyglot uploads, wrapper abuse, filename injection, BMP pixel webshell with filename truncation
  • server-side-deser.md - Java/Python/PHP deserialization and race-condition playbooks, PHP SoapClient CRLF SSRF via deserialization
  • server-side-advanced.md - Advanced SSRF, traversal, archive, parser, framework, and modern app-server issues, Nginx alias traversal
  • server-side-advanced-2.md - Docker API SSRF, Castor/XML, Apache expression reads, parser discrepancies, Windows path tricks, rogue MySQL server file read
  • server-side-advanced-3.md - Part 3 (CSAW/35C3/ASIS/PlaidCTF 2018): WAV polyglot upload, multi-slash URL path.startswith bypass, Xalan XSLT math:random() seed guess, SoapClient _user_agent CRLF method smuggling, gopher:/// no-host URL scheme bypass, SSRF credential leak via attacker-specified outbound URL
  • server-side-advanced-4.md - Part 4: WeasyPrint SSRF/file read (CVE-2024-28184), MongoDB regex/$where blind oracle, Pongo2 Go template injection, ZIP PHP webshell, basename() bypass, wget CRLF SSRF→SMTP, Gopher SSRF to MySQL blind SQLi, React Server Components Flight RCE (CVE-2025-55182), AMQP/TLS interception via sslsplit+arpspoof, CairoSVG XXE, Bazaar repo reconstruction
  • client-side.md - XSS, CSRF, cache poisoning, DOM tricks, admin bot abuse, request smuggling, paywall bypass
  • client-side-advanced.md - CSP bypasses, Unicode tricks, XSSI, CSS exfiltration, browser normalization quirks, postMessage null origin bypass
  • auth-and-access.md - Auth/authz bypasses, hidden endpoints, IDOR, redirect chains, subdomain takeover, AI chatbot jailbreaks
  • auth-and-access-2.md - Part 2 (2018-era): std::unordered_set bucket collision auth bypass, nodeprep.prepare Unicode homograph username collision, SRP A=0/A=N auth bypass, ArangoDB AQL MERGE privilege escalation
  • auth-jwt.md - JWT/JWE manipulation, weak secrets, header injection, key confusion, replay
  • auth-infra.md - OAuth/OIDC, SAML, CORS, CI/CD secrets, IdP abuse, login poisoning
  • node-and-prototype.md - Prototype pollution, JS sandbox escape, Node.js attack chains
  • web3.md - Solidity and Web3 challenge notes
  • cves.md - CVE-driven techniques you can match against challenge banners, headers, dependency leaks, or version strings
  • field-notes.md - Long-form exploit notes: quick references for SQLi, XSS, LFI, JWT, SSTI, SSRF, command injection, XXE, deserialization, race conditions, auth bypass, and multi-stage chains

Read the full file on GitHub · 153 lines

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.

  1. 11d ago First seen · 153 lines · 124 tokens per session scan B 3fd4cafdb39b

Subscribe to this mod's changes

ctf-web is a skill published in the GitHub repository ljagiello/ctf-skills (3,234 stars, last pushed 16d ago), licensed MIT. It adds 124 tokens to every session and 2,674 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it B with 2 findings (sends data to an external url, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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