Free Subdomain Takeover Checker
Free tool
Scans your DNS for dangling CNAMEs and known provider takeover fingerprints (Heroku, S3, GitHub Pages, and more) so you can reclaim them before attackers do.
- Orphaned CNAMEs
- Provider fingerprints
- Takeover indicators
No credit card requiredProduction-safe (100% passive)No setup or code required
Used by 5,000+ developers and engineering teams
What you get for free
18 core security checks via this tool, passive scans, step-by-step remediation, security score on every result.
What Essential adds at $39/mo
+17 advanced checks, continuous monitoring, daily security score history, email alerts, GitHub SAST, board-ready PDFs, SOC 2 / ISO 27001 / PCI reports.
How to prevent takeovers
- Remove stale CNAMEs/ALIAS records
- Use provider verification and auto-cleanup
- Continuously monitor DNS changes
What is subdomain takeover?
When a DNS record points to a deprovisioned resource (like an unused SaaS hostname), attackers can claim it and serve content under your subdomain.
How to fix a dangling record
The fix is not code, it's DNS hygiene. A dangling record is one that still points at a service you no longer control, so you either remove it or make it point at something you do control again:
- Open your DNS provider's dashboard (Cloudflare, Route 53, Namecheap, wherever the zone lives) and find the flagged record, typically a CNAME like
old-apppointing atmyapp.herokudns.com,something.azurewebsites.net, or a GitHub Pages hostname. - If the subdomain is dead, delete the record. This is the safe default: attackers can only claim the abandoned service while your DNS still points at it.
- If the subdomain should stay live, re-create the resource at the provider first (reclaim the Heroku app, the S3 bucket name, the Pages site), then leave the record as is.
- Check A/AAAA and ALIAS records too, not just CNAMEs. An IP that was released back to a cloud provider can be picked up by someone else.
Verify the cleanup
# Should print nothing (record deleted) or the new, claimed target
dig +short CNAME old-app.example.com
# List every CNAME in the zone you exported, to catch other stale entries
grep -i cname zonefile.txtTool-specific questions
Which providers are commonly abused?
Static hosting, CDN, and SaaS providers where resources can be reclaimed by other users. Keep your inventory up to date.
Can wildcard DNS cause issues?
Yes. Wildcards can mask stale records and broaden risk. Prefer explicit records.
How do I detect stale CNAMEs?
Maintain a DNS inventory, scan for providers' known takeover fingerprints, and remove records pointing to deprovisioned resources.
Why Barrion
Built for the engineers who already have enough to fix.
Speed
Real-time results
Instant analysis with a detailed report. You see findings as the scan runs, not after.
Coverage
Comprehensive checks
35+ checks per scan covering TLS, headers, CORS, cookies, DNS, email auth, and more, in a single pass.
Action
Step-by-step fixes
Every finding ships with the exact remediation step for your framework. Hand it to the engineer who owns the surface.
Other tools
More free checks, for the rest of your surface.
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FAQ
Frequently asked.
What is Barrion and how does it enhance website security?
Barrion is a security testing and monitoring platform for engineering teams, and it works in three ways. Passive scanning keeps a continuous, read-only watch over your live web apps and APIs. Codebase scanning connects to GitHub and checks your code for hard-coded secrets, insecure patterns and vulnerable dependencies. AI pentesting goes on the offensive, running agent-driven attacks that prove which vulnerabilities are genuinely exploitable. Every finding comes with a step-by-step fix you can ship right away.
How safe is Barrion to use for security testing?
Passive scanning and codebase scanning are completely safe to run, including against production. Passive scans only read your live app, so we never submit forms, brute-force endpoints or touch anything that changes state, and codebase scanning just reads your repository. AI pentesting is more aggressive by design, since its job is to confirm real exploits, so it runs rate-limited and non-destructive, and you approve the exact scope before a single request is sent.
What types of security issues does Barrion identify?
It depends on the surface. On your live apps, Barrion catches misconfigurations across TLS and HTTPS, security headers, cookie flags, CORS policy, DNS records, email authentication (SPF, DKIM, DMARC), network exposure and the usual web hygiene gaps. In your codebase it finds secrets committed to the repo, insecure code patterns and vulnerable dependencies. AI pentesting surfaces the exploitable stuff, like SQL injection, cross-site scripting and broken access control, each one backed by proof it can actually be exploited.
What specific security checks does Barrion perform?
For live apps it checks TLS and HTTPS configuration, HTTP security headers, cookie flags, CORS policy, DNS and email authentication records, network exposure and common web hygiene issues. In your codebase it looks for hard-coded secrets, insecure patterns and vulnerable dependencies. AI pentesting takes it further by actively chaining requests to confirm exploitable flaws. Whatever the source, findings are ranked by severity and come with clear, step-by-step remediation.
What is Barrion's smart crawling?
Smart crawling automatically discovers the pages and endpoints of your app so scans cover the surface that matters, without you manually listing every URL.
How often does Barrion perform security scans?
You can run a scan manually whenever you want. Continuous monitoring of your live apps runs on its own (weekly and up on Essential, daily on Business), codebase scans can fire on every commit or pull request, and we alert you the moment something new shows up.
Is Barrion suitable for security testing of all business sizes?
Yes. Live-app monitoring, codebase scanning through GitHub and AI pentesting all work just as well for a solo developer as for a startup, a scale-up or an enterprise security team, without adding headcount.
How does Barrion handle data security and privacy during security testing?
Live-app and codebase scans are read-only by default, and we never store or expose sensitive data from your application. AI pentests are rate-limited and non-destructive, built to confirm whether something is exploitable without altering your data or affecting availability.
What if I'm not satisfied with Barrion's security testing service?
Paid plans start with a free trial, and you can cancel anytime. If something isn't right, contact us and we'll make it work for your team.
How does Barrion help with SOC 2, ISO 27001, NIS2, and other compliance frameworks?
Barrion produces audit-ready PDF and CSV reports suitable for SOC 2, ISO 27001, PCI DSS and NIS2, ready to share with auditors, customers and your board.
Anything else? Email contact@barrion.io.