hunt-subdomain

Hunting skill for subdomain takeover vulnerabilities. Includes modern provider fingerprints — Microsoft Azure DevOps `cloudapp.azure.com` regional-pool re-issue (1-click OAuth ATO via wildcard `reply_to`, Binary Security), Zendesk help-desk takeover → email interception → password reset chain (0xprial writeup), Vercel `cname.vercel-dns.com` deleted-project takeover, plus general Fastly CDN service re-attach and S3 dangling-bucket cookie-scope techniques. Use when hunting subdomain takeover — emphasis on ATO-chain primitives (OAuth `redirect_uri`, cookie-domain, email DNS).

Quality

81%

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Securityby

Critical

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Quality

Content

77%

Reviews the quality of instructions and guidance provided to agents. Good implementation is clear, handles edge cases, and produces reliable results.

A strong, highly actionable hunting skill with executable commands, a sequenced methodology, and explicit validation gates. Its weaknesses are length/narrative padding and a monolithic structure that keeps reference-grade material (fingerprint tables, chain details, citations) inline rather than in separate bundle files.

Suggestions

Extract the provider fingerprint table and the five chain deep-dives into one-level-deep reference files (e.g. references/fingerprints.md, references/chains.md) and signal them from the body to improve navigation and token efficiency.

Trim the 'Real Impact Examples' scenarios and per-chain 'Real shape' prose to one-line pointers, keeping only the operational claim-flow steps that are not already covered in the methodology.

Dimension	Reasoning	Score
Conciseness	The body is operationally dense and avoids explaining basic concepts Claude knows, but at ~335 lines it carries narrative padding — the three 'Real Impact Examples' scenarios and the repetitive per-chain 'Real shape'/'Impact' prose could be tightened without losing actionable value.	2 / 3
Actionability	Provides copy-paste-ready, executable commands throughout — 'subfinder -d target.com -all', 'cat subdomains.txt \| dnsx -a -cname', 'subjack -w subdomains.txt -t 100 -timeout 30 -ssl', 'aws s3api head-bucket --bucket <name>', and a working bulk-CNAME bash loop — far exceeding the pseudocode threshold.	3 / 3
Workflow Clarity	A clearly sequenced 9-step methodology with explicit validation checkpoints (step 4 manual verification, 'Gate 0 Validation' with a 10-minute reproducibility test, and the hard rule 'If you cannot show the provider resource is currently unclaimed and claimable, it is not a valid report') gives strong error-recovery feedback loops.	3 / 3
Progressive Disclosure	Sections are well-organized, but the file is a ~335-line monolith with no bundle files: the provider fingerprint list, the five chain deep-dives, and the disclosed-report citations are all inline content that would be better split into one-level-deep reference files for navigation.	2 / 3
	Total	10 / 12 Passed

Description

85%

Based on the skill's description, can an agent find and select it at the right time? Clear, specific descriptions lead to better discovery.

A highly specific, third-person description with an explicit 'Use when' trigger and a clear niche. Its main weakness is trigger-term breadth — it leans on a single natural phrase plus internal writeup citations rather than covering the common variations a user would actually say.

Suggestions

Replace writeup-author citations ('0xprial writeup', 'Binary Security') with natural trigger terms like 'dangling CNAME', 'DNS takeover', or 'CNAME takeover' so the description matches how users actually phrase the need.

Add 1-2 common variation keywords alongside 'subdomain takeover' to broaden trigger coverage without losing specificity.

Dimension	Reasoning	Score
Specificity	Lists multiple concrete actions and provider-specific primitives — 'Azure DevOps cloudapp.azure.com regional-pool re-issue', 'Zendesk help-desk takeover → email interception → password reset chain', 'Vercel cname.vercel-dns.com deleted-project takeover', 'Fastly CDN service re-attach', 'S3 dangling-bucket cookie-scope', plus ATO-chain primitives (OAuth redirect_uri, cookie-domain, email DNS).	3 / 3
Completeness	Explicitly answers both what ('Hunting skill for subdomain takeover vulnerabilities...') and when ('Use when hunting subdomain takeover'), satisfying the explicit-trigger requirement that would otherwise cap this dimension at 2.	3 / 3
Trigger Term Quality	The core natural term 'subdomain takeover' is present, but coverage of common variations a hunter would say ('dangling CNAME', 'DNS takeover', 'CNAME takeover') is absent, and the description is padded with citation labels ('0xprial writeup', 'Binary Security') that are not trigger terms a user would naturally say.	2 / 3
Distinctiveness Conflict Risk	The trigger 'hunting subdomain takeover' names a clear, narrow niche distinct from sibling hunt-* skills; while ATO-chain primitives overlap with hunt-oauth, the activation trigger is specific enough to avoid firing for the wrong skill.	3 / 3
	Total	11 / 12 Passed

Validation

93%

Warnings & errors only

Checks the skill against the spec for correct structure and formatting. All validation checks must pass before discovery and implementation can be scored.

Validation — 15 / 16 Passed

Validation for skill structure

Criteria	Description	Result
frontmatter_unknown_keys	Unknown frontmatter key(s) found; consider removing or moving to metadata	Warning

	Total	15 / 16 Passed

Repository: elementalsouls/Claude-BugHunter
Path: skills/hunt-subdomain/SKILL.md
Commit: 6b9c96e

Reviewed: 2 days ago

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