hunt-subdomain

hunt-subdomain is a skill for Claude Code, Codex from adriannoes/awesome-agentic-ai. It costs 30 tokens per session (3,238 once invoked), scanned A, original, MIT.

A security-testing guide for finding subdomain takeover, where an abandoned external service can be claimed and used under a company’s domain.

In plain words
What is it for?
Use it to inspect DNS records, abandoned cloud or SaaS integrations, and unused preview, staging, development, or documentation subdomains.
Why use it?
It helps uncover trusted subdomains that could host attacker content, support phishing, or affect sign-in and OAuth flows.

Skill for Claude CodeCodex

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

Good fit Use it to inspect DNS records, abandoned cloud or SaaS integrations, and unused preview, staging, development, or documentation subdomains.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/adriannoes/awesome-agentic-ai/hunt-subdomain
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 adriannoes/awesome-agentic-ai --skill hunt-subdomain
Clone the repo
git clone --depth 1 https://github.com/adriannoes/awesome-agentic-ai

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-subdomain

README.md
[![agentmods](https://agentmods.dev/badge/skills/adriannoes/awesome-agentic-ai/hunt-subdomain/github.svg)](https://agentmods.dev/skills/adriannoes/awesome-agentic-ai/hunt-subdomain)
Your own site
<a href="https://agentmods.dev/skills/adriannoes/awesome-agentic-ai/hunt-subdomain"><img src="https://agentmods.dev/badge/skills/adriannoes/awesome-agentic-ai/hunt-subdomain/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-subdomain

Your own site · 80×15
<a href="https://agentmods.dev/skills/adriannoes/awesome-agentic-ai/hunt-subdomain"><img src="https://agentmods.dev/badge/skills/adriannoes/awesome-agentic-ai/hunt-subdomain.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 3,238 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
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 $0.03238
Opus 5 $0.00015 $0.01619
Sonnet 5 $0.00006 $0.00648
Haiku 4.5 $0.00003 $0.00324

Measured 9d ago against content hash ad6e2afab3b2, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

hunt-subdomain scanned grade A with 1 finding 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.

Makes network callslowCapability

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

- `curl -sk https://subdomain.target.com` — check for provider error string
cursor-claude-codex/skills/bug-hunter/skills/hunt-subdomain/SKILL.md · 239 lines

How it starts

The opening of the file, as written. The whole thing — 239 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Crown Jewel Targets

Subdomain takeover is high-value because it allows an attacker to serve content from a trusted, company-owned domain — bypassing browser same-origin trust, phishing filters, and user skepticism simultaneously.

Highest payout contexts:

  • Subdomains of major SaaS brands (Shopify, Snapchat, Mozilla, Yelp) where the trusted domain has user session context
  • CDN-backed subdomains (Fastly, CloudFront) where CNAME points to unclaimed origins
  • Third-party service integrations: UserVoice, WordPress.com, GitHub Pages, GitLab Pages, Heroku, Zendesk
  • Preview/staging/dev subdomains (new., preview., course., delivery., addons-preview.) — abandoned after feature launches
  • Subdomains used for OAuth redirect URIs or SSO endpoints — these pay highest

Asset types that matter most:

  • CNAME records pointing to deprovisioned third-party services
  • NS delegations to abandoned zones
  • A records pointing to unallocated cloud IPs (less common)
  • GitLab/GitHub Pages with unclaimed project namespaces

Attack Surface Signals

DNS signals:

  • CNAME pointing to *.github.io, *.gitlab.io, *.fastly.net, *.herokudns.com, *.wordpress.com, *.uservoice.com, *.zendesk.com, *.s3.amazonaws.com, *.azurewebsites.net, *.netlify.app
  • NXDOMAIN or SERVFAIL on the CNAME target while the parent record still exists
  • NS records delegating to registrars where the zone is no longer registered

HTTP response signals:

  • "There isn't a GitHub Pages site here"
  • "NoSuchBucket" (S3)
  • "The specified bucket does not exist"
  • "No such app" (Heroku)
  • "Sorry, this shop is currently unavailable" (Shopify)
  • "This UserVoice subdomain is available"
  • "Do you want to register" (any domain parking page)
  • HTTP 404 with provider-specific error templates
  • Fastly: "Fastly error: unknown domain"

Tech stack signals:

  • Response headers: X-Served-By: cache-* (Fastly), X-GitHub-Request-Id, Server: Netlify
  • CNAME chain resolving to provider infrastructure but returning provider 404
  • SSL cert issued to provider wildcard (*.fastly.net) rather than company domain

Read the full file on GitHub · 239 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 · 239 lines · 30 tokens per session scan A ad6e2afab3b2

Subscribe to this mod's changes

hunt-subdomain is a skill published in the GitHub repository adriannoes/awesome-agentic-ai (57 stars, last pushed 14d ago), licensed MIT. It adds 30 tokens to every session and 3,238 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (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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