webvuln

A hands-on guide for testing specific websites or API endpoints for security weaknesses. It covers issues such as accessing another user’s data, injection attacks, login flaws, server-side request forgery, and known software vulnerabilities.

In plain words
What is it for?
Use it after discovering hosts and endpoints to test access controls, authentication, input handling, request forwarding, and known vulnerable software. It helps produce a reproducible proof and a clear impact statement.
Why use it?
It keeps security testing focused on real targets and requires proof of an actual problem and its effect. This helps avoid reporting theoretical issues or using heavy scanners before they are needed.

Skill for Claude CodeCodex

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/pentesterflow/agent/webvuln
Any agent
npx skills add PentesterFlow/agent --skill webvuln
Clone the repo
git clone --depth 1 https://github.com/PentesterFlow/agent

Made for: Claude Code, Codex.

Per session 53 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,189 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 2 findings. 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.

ModelPer sessionOnce invoked
Fable 5 $0.00053 $0.01189
Opus 5 $0.00026 $0.00594
Sonnet 5 $0.00011 $0.00238
Haiku 4.5 $0.00005 $0.00119

Measured 2d ago against content hash 1df7b5f1a110, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

webvuln 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 2d 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.

Cloud metadata endpointmediumServer-side request forgery

One request to 169.254.169.254 can return temporary IAM credentials.

Any parameter that takes a URL or hostname: try `http://127.0.0.1`, `http://169.254.169.254/latest/meta-data/`, and an out-of-band canary the user provides. Compare response timings and bodies with curl `-w "%{time_total

Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.

Makes network callslowCapability

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

Default to curl and the built-in `http` tool. Do not pull in heavy scanners (nuclei, sqlmap, ffuf, etc.) unless the user explicitly asks for them or you have manually confirmed a bug and need a scanner only to characteri
skills/webvuln/SKILL.md · 88 lines

How it starts

The opening of the file, as written. The whole thing — 88 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Web vuln hunting playbook

You are testing specific endpoints the user has handed you (or that came out of the recon skill). Every finding must come with a real PoC and a concrete impact statement — no theoretical bugs.

Default to curl and the built-in http tool. Do not pull in heavy scanners (nuclei, sqlmap, ffuf, etc.) unless the user explicitly asks for them or you have manually confirmed a bug and need a scanner only to characterize the bug class.

Execution rule: substitute real target values before running commands. Never write literal placeholders such as <TARGET>, <vulnerable-path>, or <PoC body> to files. If a value is unknown, ask once or derive it from /target.

1. Triage the target

Fetch the landing page with the http tool or curl. Note:

  • Framework / language signals (cookies, headers, error pages)
  • Authentication scheme (cookie, Bearer, basic)
  • API style (REST / GraphQL / gRPC)
  • Anything that suggests a known CVE family (versioned banner, vendor product name)

If you spot a versioned product, immediately web_search "<product> <version> CVE" and web_fetch the top advisory. Reproduce the CVE manually with curl before reporting.

2. Known-CVE pass (manual, curl-driven)

For each suspected CVE pulled from the advisory, craft the curl that proves it — single request when possible:

TARGET="https://app.example.com" # replace with the scoped target before running
curl -ksS -X POST "$TARGET/vulnerable-path" \
  -H 'Content-Type: application/json' \
  -d '{"replace":"with-real-poc-body"}' \
  -w "\nHTTP %{http_code}  size=%{size_download}  time=%{time_total}\n"

If the advisory describes a recognizable pattern (template injection, deserialization, etc.) and the user has explicitly authorized broader scanning, then — and only then — reach for nuclei against the single host. Otherwise stay manual.

3. Auth + access control (IDOR / BAC)

  • Identify any numeric or UUID identifiers in the URL path or query (/api/users/12345, /orders/?id=...).
  • With user-provided session A, fetch a resource you own.
  • Swap the identifier to another user's value (or use a second session from the user) and replay with curl or the http tool.
  • A 200 with foreign data = IDOR. Capture the curl one-liner and the response excerpt into findings/idor-<endpoint>.txt.

Read the full file on GitHub · 88 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. 2d ago First seen · 88 lines · 53 tokens per session scan B 1df7b5f1a110

Subscribe to this mod's changes

webvuln is a skill published in the GitHub repository PentesterFlow/agent (1,316 stars, last pushed 2mo ago), licensed Apache-2.0. It adds 53 tokens to every session and 1,189 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it B with 2 findings (cloud metadata endpoint, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.