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.
npx skills add UnboundCompute/security-agent-skills --skill hunting-subdomain-takeover-and-dangling-dnsgit clone --depth 1 https://github.com/UnboundCompute/security-agent-skillsWrote 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.
[](https://agentmods.dev/skills/unboundcompute/security-agent-skills/hunting-subdomain-takeover-and-dangling-dns)<a href="https://agentmods.dev/skills/unboundcompute/security-agent-skills/hunting-subdomain-takeover-and-dangling-dns"><img src="https://agentmods.dev/badge/skills/unboundcompute/security-agent-skills/hunting-subdomain-takeover-and-dangling-dns/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.
<a href="https://agentmods.dev/skills/unboundcompute/security-agent-skills/hunting-subdomain-takeover-and-dangling-dns"><img src="https://agentmods.dev/badge/skills/unboundcompute/security-agent-skills/hunting-subdomain-takeover-and-dangling-dns.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00181 | $0.02101 |
| Opus 5.5 | $0.00072 | $0.00840 |
| Sonnet 5.5 | $0.00036 | $0.00420 |
| Haiku 4.5 | $0.00018 | $0.00210 |
Grade A, and why
hunting-subdomain-takeover-and-dangling-dns scanned grade A with 0 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 1mo 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.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 141 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Hunting subdomain takeover and dangling DNS: who can claim the name you still point at
A subdomain takeover is not a source-code bug, which is exactly why source-focused reviews miss it. It is a bug in DNS state: a record still resolves, but the thing it points at is gone, and the shared provider will hand that target to whoever asks next. When an attacker claims it, they serve content on your trusted origin, with a real certificate, inheriting parent-domain cookies, allowlist and content-policy trust, and OAuth redirect standing. You hunt it by inventorying the records, resolving each target, and asking one question per record: is the target still owned, and if not, can an attacker claim it. The discipline is separating a record that merely returns a 404 from one whose target is genuinely re-registrable, because only the second is a takeover.
When to use
- You have DNS zone files, or the DNS records declared in infrastructure-as-code, for a domain in scope.
- A subdomain points at a platform host, storage bucket, content-delivery endpoint, or third-party service.
- You want to know which records are dangling and, of those, which an attacker can actually claim.
Scope check
Enumerate and fingerprint only domains you own or are authorized to assess, and never register or claim a target you do not own outside an authorized engagement, claiming it is the point of no return and can hijack live traffic. Demonstrate claimability by fingerprint, not by seizing the name. If you can't name the authorization, stop.
The loop
-
Inventory the records and resolve every target. Collect the CNAME, ALIAS, NS, and wildcard records from the zone and from any infrastructure-as-code that declares them, and resolve each to the host or service it points at. The record set is the surface; a record whose target no longer answers, or answers as unrecognized, is the lead.
-
Fingerprint the target's claim state. For each dangling-looking target, read the response the provider returns. A takeover needs two things together: a provider fingerprint that says the host is unclaimed (an unrecognized-domain page, a no-such-bucket error, a default landing that invites registration) and a provider that permits open re-registration of that name. One without the other is not a takeover.
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.
- 1mo ago First seen · 141 lines · 181 tokens per session scan A 1a255fda0d07
hunting-subdomain-takeover-and-dangling-dns is a skill published in the GitHub repository UnboundCompute/security-agent-skills (5 stars, last pushed 1mo ago), licensed MIT. It adds 181 tokens to every session and 2,101 once invoked, about $0.0007 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-05.
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