Warning: A 10-Year-Old Bug Is Still Letting Hackers Hijack URLs By CyberDudeBivash

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Executive Summary

A class of vulnerabilities first documented nearly a decade ago — broadly known as Broken Link Hijacking (BLH) — continues to haunt many organizations. Essentially, old or forgotten external URLs, scripts, subdomains, or file links that are still referenced in your live web pages but either have expired or been removed, are being automatically claimed by attackers. Once claimed, these dead endpoints become vectors for phishing, XSS, content injection, or even supply-chain compromise. Despite being “old news,” monitoring suggests that many high-traffic sites still suffer from broken/hijackable URLs, making this a persistent, under-appreciated risk.

What is Broken Link Hijacking (BLH)?

  • When a website or web-app includes a link or resource (script, style, image, subdomain, etc.) pointing to an external endpoint that is no longer valid (domain expired, repo removed, resource deleted, or DNS records floating).

  • If an attacker notices this and can claim that endpoint (or the domain/subdomain / hosting site), they can serve malicious code, takeover content, intercept data, etc.

  • Common forms include:

    1. External JS/CSS hijack via expired CDN or GitHub Pages.

    2. Expired subdomain takeover (e.g. a CNAME pointing to a Heroku app that’s been removed).

    3. Vanity / branded shortened links that expire and get reclaimed, then used for phishing or redirecting.

References: Indusface blog on BLH Indusface; recent writeups of Broken Link Hijacking mechanics. Medium+1

Why It’s Still a Problem After 10 Years

  1. Code rot & forgotten references
    Web sites evolve: pages removed, projects deprecated, static assets relocated. Yet many links to these resources remain in templates, footers, CSS/JS includes, marketing collateral, emails, etc.

  2. Domain / hosting churn
    Domains expire, cloud-hosted repos are removed, apps are decommissioned. Attackers scan for unclaimed assets with known names (subdomain, repo, slug) and grab them.

  3. High trust context
    Because the asset is hosted under a domain or platform that is considered “trusted” (same site, same company URL, same brand subdomain), when it’s hijacked it enjoys that trust. Visitors assume scripts are safe, images are benign, etc.

  4. Lack of auditing
    Traditional scanning tools often focus on XSS, SQLi, buffer overflows, etc., but forget to crawl for 404s on linked assets, dead external scripts, or subdomains pointing to nowhere.

  5. Repetition and scale
    Every such broken link is a potential risk, multiplied by the number of domains, subdomains, and assets large organizations maintain. One small overlooked broken link can be enough.

Real-World Examples & Attack Scenarios

  • A high-traffic site linking to a Heroku subdomain (no longer in use). Attacker claims that herokuapp URL, uploads a malicious script, then achieves XSS via the main site loading the script. (From recent BLH reports) Medium+1

  • Expired shortened links (e.g. vanity Bit.ly or branded short domains) used in marketing emails still pointing to resources. Attacker reclaims the link slug and redirects recipients to phishing or exploit pages. Medium+1

Risks & Impact

Attack TypeImpact
Stored XSS / Script hijackingPersistent injection of malicious JS (credential theft, session hijack, malware delivery)
Defacement / brand damageSite content altered, phishing content displayed under trusted domain
Supply-chain compromiseTrusted assets (scripts/css) can load malicious payloads for all visitors
Data interceptionVia scripts or redirects on trusted endpoints
Reputational, legal, compliance lossIf sensitive data or user trust is violated

Threat Model

  • Adversary: Attacker who can monitor DNS / domain expiration / hosting repo removal; claims expired domain or hosting service slot.

  • Requirements:

    1. The target site includes a link to that external resource (script, CSS, image, domain) still in production.

    2. The external resource is unprotected (can be claimed / hosted by anyone).

  • Privilege gained: Depends on resource type: from moderate (malicious JS) to high (stealing tokens, session-cookies, credentials).

Detection & Defense Strategies

  1. Asset Link Auditing

    • Crawl website for external resources (scripts, CSS, images, iframes etc.).

    • Detect broken links (HTTP 404 / DNS not resolved / hosting “unowned”)

  2. Subdomain / Repo Takeover Monitoring

    • Monitor CNAMEs, subdomains pointing to external platforms (Heroku, Netlify, GitHub Pages, etc.).

    • Use tools or services that notify when subdomain is “dangling” (pointing to a non-existent app).

  3. Content Security Policy (CSP)

    • Restrict which domains your site can load scripts/resources from. If an external resource becomes hijacked, CSP can limit damage.

  4. Remove or replace stale links

    • When a resource is deprecated, remove the reference or host the resource locally if needed.

  5. Security reviews / pen tests including broken link vectors

    • Include checks for BLH in security audits / bug bounty scopes.

  6. DNS / Domain Monitoring

    • Expiration monitoring for domains/subdomains used in site.

    • Warnings or alerts ex: “subdomain pointing to removed Heroku app” etc.

Aged Bug or Persistent Threat?

Although the mechanics of BLH have been known for many years (often mentioned in security blogs, bug bounty forums), the threat is still very alive. The difference is scale: as web infrastructure becomes more distributed (microservices, multiple static sites, asset CDNs, many subdomains), the chances increase that something, somewhere, has been forgotten.

CyberDudeBivash Action-Checklist

  •  Run a crawler over all web properties to list external JS/CSS/image includes → check for broken / unresponsive endpoints.

  •  Audit DNS entries / CNAMEs → find subdomains pointing to removed hosts or deprecated services.

  •  Remove or replace links to expired domains, orphaned external scripts.

  •  Apply CSP to limit the trust boundary for loaded resources.

  •  Monitor domain/subdomain expiration and hosting platform decommission events.

  •  When using URL shorteners or custom branded domains, ensure renewals are handled and expired slugs cannot be reclaimed by attackers.

    Affiliate Toolbox (clearly disclosed)

    Disclosure: If you buy via the links below, we may earn a commission at no extra cost to you. These items supplement (not replace) your security controls. This supports CyberDudeBivash in creating free cybersecurity content.

    🌐 cyberdudebivash.com | cyberbivash.blogspot.com

Conclusion

Broken Link Hijacking may seem like an “old bug” — but it continues to provide low-friction, high-impact attack vectors. If your organization doesn’t have a program for auditing external links and resources, you’re probably exposing yourself already. Taking steps now to reduce stale dependencies, enforce safer policies, and monitor for reclamable assets can dramatically cut your risk of hijack, phishing, or content compromise.


Affiliate Toolbox (clearly disclosed)

Disclosure: If you buy via the links below, we may earn a commission at no extra cost to you. These items supplement (not replace) your security controls. This supports CyberDudeBivash in creating free cybersecurity content.

🌐 cyberdudebivash.com | cyberbivash.blogspot.com

#CyberDudeBivash #BrokenLinkHijacking #URLHijack #WebSecurity #SupplyChain #ThreatIntel #WebAppSec #Infosec


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