html-injection-testing

html-injection-testing is a skill for Claude Code, Codex from tmolavi/mcp-agent-skills-hub. It costs 44 tokens per session (3,481 once invoked), scanned A, a copy of html-injection-testing, MIT.

A guide for finding HTML injection flaws, where untrusted input is displayed as webpage markup. These flaws can alter a page or create fake forms, so testing must be authorised.

In plain words
What is it for?
Use it during authorised security assessments to test input handling, document injection points and proof of impact, and recommend validation fixes.
Why use it?
It helps reveal places where an application displays user input without sufficient filtering and explains the possible security impact.

Skill for Claude CodeCodex

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

Good fit Use it during authorised security assessments to test input handling, document injection points and proof of impact, and recommend validation fixes.

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Install with agentmods
npx agentmods add skills/tmolavi/mcp-agent-skills-hub/html-injection-testing
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 tmolavi/mcp-agent-skills-hub --skill html-injection-testing
Clone the repo
git clone --depth 1 https://github.com/tmolavi/mcp-agent-skills-hub

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 html-injection-testing

README.md
[![agentmods](https://agentmods.dev/badge/skills/tmolavi/mcp-agent-skills-hub/html-injection-testing/github.svg)](https://agentmods.dev/skills/tmolavi/mcp-agent-skills-hub/html-injection-testing)
Your own site
<a href="https://agentmods.dev/skills/tmolavi/mcp-agent-skills-hub/html-injection-testing"><img src="https://agentmods.dev/badge/skills/tmolavi/mcp-agent-skills-hub/html-injection-testing/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 html-injection-testing

Your own site · 80×15
<a href="https://agentmods.dev/skills/tmolavi/mcp-agent-skills-hub/html-injection-testing"><img src="https://agentmods.dev/badge/skills/tmolavi/mcp-agent-skills-hub/html-injection-testing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 44 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,481 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 2 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin 86% copy Near-identical to another mod 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 $0.00044 $0.03481
Opus 5 $0.00022 $0.01741
Sonnet 5 $0.00009 $0.00696
Haiku 4.5 $0.00004 $0.00348

Measured 9d ago against content hash e754642d59fa, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

html-injection-testing scanned grade A 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 9d 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 URLlowData 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 -X POST -d "comment=<div style='color:red'>Malicious Content</div>" \

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.

curl "http://target.com/search?q=<h1>Test</h1>"
Origin

This is a copy

86% identical to html-injection-testing — 14 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.

skills/html-injection-testing/SKILL.md · 505 lines

How it starts

The opening of the file, as written. The whole thing — 505 lines — stays where its author put it; the contents beside it link to each section on GitHub.

AUTHORIZED USE ONLY: Use this skill only for authorized security assessments, defensive validation, or controlled educational environments.

HTML Injection Testing

Purpose

Identify and exploit HTML injection vulnerabilities that allow attackers to inject malicious HTML content into web applications. This vulnerability enables attackers to modify page appearance, create phishing pages, and steal user credentials through injected forms.

Prerequisites

Required Tools

  • Web browser with developer tools
  • Burp Suite or OWASP ZAP
  • Tamper Data or similar proxy
  • cURL for testing payloads

Required Knowledge

  • HTML fundamentals
  • HTTP request/response structure
  • Web application input handling
  • Difference between HTML injection and XSS

Outputs and Deliverables

  1. Vulnerability Report - Identified injection points
  2. Exploitation Proof - Demonstrated content manipulation
  3. Impact Assessment - Potential phishing and defacement risks
  4. Remediation Guidance - Input validation recommendations

Core Workflow

Phase 1: Understanding HTML Injection

HTML injection occurs when user input is reflected in web pages without proper sanitization:

<!-- Vulnerable code example -->
<div>
    Welcome, <?php echo $_GET['name']; ?>
</div>

<!-- Attack input -->
?name=<h1>Injected Content</h1>

<!-- Rendered output -->
<div>
    Welcome, <h1>Injected Content</h1>
</div>

Key differences from XSS:

  • HTML injection: Only HTML tags are rendered
  • XSS: JavaScript code is executed
  • HTML injection is often stepping stone to XSS

Attack goals:

  • Modify website appearance (defacement)
  • Create fake login forms (phishing)
  • Inject malicious links
  • Display misleading content

Phase 2: Identifying Injection Points

Map application for potential injection surfaces:

1. Search bars and search results
2. Comment sections
3. User profile fields
4. Contact forms and feedback
5. Registration forms
6. URL parameters reflected on page
7. Error messages
8. Page titles and headers
9. Hidden form fields
10. Cookie values reflected on page

Read the full file on GitHub · 505 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. 9d ago First seen · 505 lines · 44 tokens per session scan A e754642d59fa

Subscribe to this mod's changes

html-injection-testing is a skill published in the GitHub repository tmolavi/mcp-agent-skills-hub (8 stars, last pushed 17d ago), licensed MIT. It adds 44 tokens to every session and 3,481 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 2 findings (sends data to an external url, makes network calls). It is 86% identical to html-injection-testing, differing in 14 lines, and is treated as a copy.

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