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Subdomain Takeover

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H-mmer
subdomain-takeover

Subdomain Takeover specialist (H1 #145). Use for finding dangling DNS records pointing to unclaimed cloud resources, expired services, or deprovisioned infrastructure.

Overview

PublisherH-mmer
Repositorypentest-agents
Skill namesubdomain-takeover
Stars
999
Forks
188
Bundled files
Instructions only
Links
Skill sourceRepository
  • Markdown instructions

    A SKILL.md file the model loads on demand, so it only costs tokens when a request actually matches.

  • Works with any LLM

    AI skills are plain Markdown, not provider-specific code, so this works with GPT, Claude, Gemini, Grok, or a local model.

  • Self-contained

    Everything the model needs lives in the instructions — no extra files to sync.

  • Open source

    Published by H-mmer on GitHub. Read the source before you install it.

Installation

Install the Subdomain Takeover AI skill in TypingMind to use it with any LLM, or drop it into another agent that reads SKILL.md.

1

Install in TypingMind

TypingMind installs a skill straight from its GitHub folder — it reads SKILL.md, bundles the resource files, and stores the result locally.

  1. Open the app and go to Plugins → Skills.
  2. Choose "Install from GitHub".
  3. Paste the skill folder URL below and confirm.
    https://github.com/H-mmer/pentest-agents/tree/main/providers/openclaw/.agents/skills/agent-subdomain-takeover
  4. Enable the skill in any chat where you want it available.
Plugins → Skills → Add skill → From GitHub URL, then paste the folder URL and press Continue.
2

Install in another agent

Any agent that reads the Agent Skills format can use this skill — copy the folder into that agent's skills directory.

Claude Code — .claude/skills
git clone --depth 1 https://github.com/H-mmer/pentest-agents.git /tmp/pentest-agents
mkdir -p .claude/skills
cp -r /tmp/pentest-agents/providers/openclaw/.agents/skills/agent-subdomain-takeover .claude/skills/subdomain-takeover
Restart Claude Code after copying so it picks up the new skill.

Use it in TypingMind

Enable Subdomain Takeover in any TypingMind chat and the model takes it from there. Its name and description sit in the system prompt, and the moment a request matches, the model loads the full instructions itself — you never invoke it by hand, and it costs no tokens until it is actually used.

The model loads Subdomain Takeover on its own as soon as a request matches it.

Works with any AI model

AI skills are plain Markdown instructions rather than provider-specific code, so Subdomain Takeover is not tied to the model it was written for. Install it once in TypingMind and use it with GPT-5, Claude, Gemini, Grok, DeepSeek, Mistral, Llama, or a local model you run yourself — all on your own API keys.

  • Loaded only when it is needed

    The system prompt carries just the name and description. The instructions are fetched on the first matching request, so an idle skill costs nothing.

  • Switch models mid-chat

    Because the skill is instructions rather than code, changing model does not break it — the next model reads the same SKILL.md.

Skill instructions

This is the SKILL.md content the model loads. Read it before installing — a skill is instructions your model will follow.

CONTEXT: You are operating within an authorized bug bounty program. All targets have been verified in-scope via the official platform API. Follow responsible disclosure practices.

MANDATORY: Research First (not optional)

Before testing subdomain takeover, you MUST call:

  • search_techniques with "Subdomain-Takeover" — proven exploitation techniques
  • search_payloads with "Subdomain-Takeover" — working payloads and bypass variants

Read the returned content and incorporate proven techniques into your plan before making any HTTP requests. Skipping this step wastes time reinventing known tricks and causes duplicate submissions. If the writeup MCP is unreachable, fall back to rules/payloads.md.

You are a subdomain takeover specialist for authorized testing.

Before probing: check vendor status

Read rules/vendor-status.md before testing any CNAME. Patched services (e.g. Azure App Service *.azurewebsites.net) are reserved indefinitely by the vendor — skip them. The cooldown table tells you which services still have a claimable window and which require policy clearance first.

Methodology

  1. Enumerate subdomains: Use recon agent output or run subfinder/amass
  2. Check CNAME records: dig CNAME sub.target.com
  3. Identify dangling records: CNAME pointing to service that returns NXDOMAIN or specific error
  4. Verify claimability: Can the resource be registered/claimed?

Vulnerable Services (CNAME → error signature)

  • AWS S3: *.s3.amazonaws.com → "NoSuchBucket"
  • GitHub Pages: *.github.io → 404 with GitHub branding
  • Heroku: *.herokuapp.com → "No such app"
  • Shopify: *.myshopify.com → "Sorry, this shop is currently unavailable"
  • Fastly: *.fastly.net → "Fastly error: unknown domain"
  • Ghost: *.ghost.io → "The thing you were looking for is no longer here"
  • Pantheon: *.pantheonsite.io → 404 specific message
  • Tumblr: *.tumblr.com → "There's nothing here"
  • WordPress.com: *.wordpress.com → "doesn't exist"
  • Zendesk: *.zendesk.com → "Help Center Closed"

DO NOT WASTE TIME ON (patched by provider)

  • Azure *.azurewebsites.net — Microsoft reserves deprovisioned App Service hostnames. Takeover is NOT possible anymore. Skip this vector entirely; do not test, do not report. Any NXDOMAIN/404 on *.azurewebsites.net is not claimable. This includes *.scm.azurewebsites.net and all App Service variants.

Tools

subjack, nuclei -t takeovers/, can-i-take-over-xyz reference

Output: H1 Weakness #145

Report as "Subdomain Takeover" with the CNAME chain, error evidence, and claim proof (or claim attempt on non-prod).

Brain Integration

Before starting, check your memory for brain briefings. Skip EXHAUSTED vectors. Focus on ACTIVE leads. After completing, label every finding: CONFIRMED, POTENTIAL, or EXHAUSTED with failure reasons and attempt counts.

Top-Tier Operator Standard

Subdomain takeover needs provider-specific claimability, not just a dangling CNAME.

  • Identify provider, canonical error, resource type, and whether the service still allows claiming that exact hostname.
  • Prefer non-prod or safe proof methods. Do not claim production assets unless policy explicitly allows it.
  • Check wildcard DNS, CDN fallback, stale A/AAAA records, apex flattening, and provider account ownership constraints.
  • Kill stale fingerprints for providers that patched takeover, non-claimable custom domains, and assets outside scope.
  • Record DNS chain, provider evidence, claimability proof, safety decision, and exact remediation.

Frequently asked questions

What does the Subdomain Takeover AI skill do?

Subdomain Takeover specialist (H1 #145). Use for finding dangling DNS records pointing to unclaimed cloud resources, expired services, or deprovisioned infrastructure.

Why use Subdomain Takeover on TypingMind?

Because you install it once and use it with any model. Subdomain Takeover is plain Markdown rather than provider-specific code, so the same skill runs on GPT-5, Claude, Gemini, Grok, or a local model — and you can switch model mid-chat without it breaking. TypingMind runs on your own API keys, so you pay providers directly instead of a per-seat subscription, and your skills and chats stay in your own storage.

How do I install Subdomain Takeover in TypingMind?

Open Plugins → Skills → Install from GitHub in TypingMind and paste https://github.com/H-mmer/pentest-agents/tree/main/providers/openclaw/.agents/skills/agent-subdomain-takeover. TypingMind reads its SKILL.md and installs it as a skill you can enable per chat.

Which AI models can use Subdomain Takeover?

Any model you connect in TypingMind. AI skills are plain Markdown instructions rather than provider-specific code, so GPT, Claude, Gemini, Grok, and local models can all load this skill when a request matches it.

How many AI models can I use with Subdomain Takeover?

As many as you like. As long as a model supports skills, you can use Subdomain Takeover with it — GPT, Claude, Gemini, Grok, DeepSeek, Mistral, Llama and more — all on TypingMind with your own API keys.

Is the Subdomain Takeover AI skill free?

It is published on GitHub by H-mmer. Check the repository for licensing terms. You only pay your own AI provider for the tokens you use.

What are AI skills?

An AI skill is a reusable instruction bundle that teaches an AI model how to do one specific task. It follows the open Agent Skills format: a SKILL.md file with a name and description, plus any scripts, templates or reference files the model may need. The model reads the instructions only when your request matches the skill, so an installed skill costs nothing until it is used.

How are AI skills different from plugins or MCP servers?

A plugin or MCP server gives a model new tools to call — code that runs somewhere and returns a result. An AI skill gives the model knowledge and process instead: how to approach a task, which steps to follow, what good output looks like. Skills are plain Markdown, so they need no server, no API key and no runtime, and they work with any model.

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