hunt-xss

hunt-xss is a skill for Claude Code, Codex from uphiago/recon-skills. It costs 30 tokens per session (7,464 once invoked), scanned C, original, MIT.

A security-testing guide for finding cross-site scripting (XSS), where attacker-controlled input runs as code in another user's web browser.

In plain words
What is it for?
It is for testing forms, URLs, uploads, search fields, and pages built with JavaScript frameworks for browser-based code injection.
Why use it?
It helps distinguish harmless text reflection from real XSS by checking how the application places and escapes user input.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit It is for testing forms, URLs, uploads, search fields, and pages built with JavaScript frameworks for browser-based code injection.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/uphiago/recon-skills/hunt-xss
About the project

Recon Skills is a pack of security-testing skills covering reconnaissance, web applications, APIs, authentication, vulnerability validation, cloud infrastructure, and reporting. Security professionals use it for authorized assessments of systems they own or have written permission to test. The catalogue entries are individual skills from the pack.

uphiago/recon-skills · 1,254 stars · on GitHub · hiago.sh

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 uphiago/recon-skills --skill hunt-xss
Clone the repo
git clone --depth 1 https://github.com/uphiago/recon-skills

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.

agentmods badge for hunt-xss

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

Your own site · 80×15
<a href="https://agentmods.dev/skills/uphiago/recon-skills/hunt-xss"><img src="https://agentmods.dev/badge/skills/uphiago/recon-skills/hunt-xss.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 30 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 7,464 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 2 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • 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 Privilege Escalation · line 401
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 402
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • medium Excessive Agency · line 357
    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.
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 $0.00030 $0.07464
Opus 5 $0.00015 $0.03732
Sonnet 5 $0.00006 $0.01493
Haiku 4.5 $0.00003 $0.00746

Measured 8d ago against content hash bc878787d412, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade C, and why

hunt-xss scanned grade C 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 8d 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.

Encoded or obfuscated payloadhighSupply chain

base64 or hex that is decoded and executed hides what actually runs from anyone reading the file.

<svg onload=eval(atob('YWxlcnQoMSk='))>

Makes network callslowCapability

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

curl --max-time 30 --connect-timeout 10 -sk "https://target.com/search?q=XSSCANARY" | grep -i "XSSCANARY"
redteam/hunt-xss/SKILL.md · 488 lines

How it starts

The opening of the file, as written. The whole thing — 488 lines — stays where its author put it; the contents beside it link to each section on GitHub.

When to Use

Use when the target has any endpoint where user input is reflected in HTML output, processed by a JavaScript framework, or stored for later display. XSS is the foundational client-side vulnerability class — it enables session hijacking, data theft, phishing, and account takeover. Every form, search field, URL parameter, file upload, and user-controlled field is a candidate. Highest-value targets: admin panels, OAuth sign-in pages, markdown/wiki renderers, email templates, file upload endpoints (SVG/HTML), and help/documentation sites with looser security posture.

⚠️ CRITICAL: Presence ≠ Exploitation

Reflection of HTML tags does NOT mean XSS is exploitable. Modern frameworks escape text by default. Before calling a finding XSS, you MUST verify the sink:

Framework Default Behavior XSS Possible Only With
React/JSX Escapes all text dangerouslySetInnerHTML, innerHTML on refs
Vue Escapes {{ }} v-html directive
Angular Escapes {{ }} [innerHTML] binding
Svelte Escapes { } {@html} tag
Next.js RSC Escapes JSX text dangerouslySetInnerHTML in components
Plain HTML/JS Does NOT escape innerHTML, document.write(), eval()

XSS verification checklist:

  1. ✅ Payload is REFLECTED/STORED in response (presence)
  2. ✅ Payload appears in a RENDERABLE context (sink check)
  3. ✅ Payload EXECUTES in browser (proof of exploitation)

If step 1 passes but step 2 fails → LOW: HTML storage without exploitable sink. The React ecosystem alone prevents ~90% of apparent XSS because JSX auto-escapes.

How to Check for Sinks:

# In JS bundles — search for dangerous rendering patterns
grep -rEn 'dangerouslySetInnerHTML|innerHTML|outerHTML|v-html|\[innerHTML\]|\{@html\}|insertAdjacentHTML|document\.write\(|eval\(' /tmp/target_js/

# If NONE appear near the reflected field → NOT exploitable XSS
# If found → verify the specific field reaches that sink

Read the full file on GitHub · 488 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. 8d ago First seen · 488 lines · 30 tokens per session scan C bc878787d412

Subscribe to this mod's changes

hunt-xss is a skill published in the GitHub repository uphiago/recon-skills (1,254 stars, last pushed 10d ago), licensed MIT. It adds 30 tokens to every session and 7,464 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it C with 2 findings (encoded or obfuscated payload, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

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