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web-subdomain-takeover

Subdomain takeover via dangling DNS/CNAME — GitHub Pages, Heroku, Azure, Fastly, Shopify, Netlify, Surge, Tumblr, Beanstalk, Zendesk, etc.

packages/decepticon/decepticon/skills/standard/recon/web-recon/subdomain-takeover/SKILL.md

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Network or broad shell
Last checked
Nov 8, 2026

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Repository last updated
Nov 7, 2026
License
Apache-2.0

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# Subdomain Takeover (Dangling DNS / CNAME)

A subdomain CNAMEs to a SaaS provider (GitHub Pages, Heroku, S3, etc.) but the underlying tenant has been deleted, expired, or never claimed. Whoever registers the orphaned tenant name controls a trusted `*.<TARGET>` origin. Severity is almost always **High → Critical** because the attacker inherits the parent domain's cookie scope, CORS allowlist, OAuth `redirect_uri` whitelist, CSP `*.<TARGET>` allowance, and reputation.

## 1. Asset surface — enumerate every subdomain

```bash
# Passive (no traffic to target)
subfinder -d <TARGET> -all -silent -o subs.txt
amass enum -passive -d <TARGET> -o subs.amass.txt
assetfinder --subs-only <TARGET> >> subs.txt
findomain -t <TARGET> -q >> subs.txt
curl -s "https://crt.sh/?q=%25.<TARGET>&output=json" | jq -r '.[].name_value' | tr '\n' '\n' | sort -u >> subs.txt
sort -u subs.txt -o subs.txt