Full Report
Learn how a minor DNS misconfiguration can quickly become a major supply chain threat and how to protect your organization from such threats.
Analysis Summary
# Vulnerability: Subdomain Takeovers via Dangling DNS Records
## CVE Details
- CVE ID: Not Listed in Source
- CVSS Score: Not Specified ([Severity Not Specified])
- CWE: Not Explicitly Listed (Related to misconfiguration, potentially CWE-404: Improper Resource Closure or CWE-427: Use of a Weak/Vulnerable Third-Party Component if supply chain exploitation occurs)
## Affected Systems
- Products: Any application or service relying on DNS records (CNAME, NS, MX, A, AAA records) pointing to external or internal resources (SaaS providers, Cloud service resources like AWS S3 buckets, etc.).
- Versions: Not applicable; this is a configuration/lifecycle management issue, not a software version flaw.
- Configurations: Subdomains where the associated DNS record (e.g., CNAME) points to a resource that has since been deprovisioned, expired, or whose subscription lapsed (e.g., an abandoned SaaS trial endpoint or a deleted cloud storage bucket).
## Vulnerability Description
This vulnerability stems from "Dangling DNS," which occurs when a DNS record for a subdomain (like a CNAME record pointing to a SaaS endpoint or a resource record pointing to a deleted cloud resource such as an AWS S3 bucket) is not removed or updated after the target resource is terminated or expires. An attacker can then register the previously used external name (e.g., register the Zendesk trial name or create a new S3 bucket with the same name) and hijack traffic intended for the legitimate subdomain. This can lead to accessing sensitive data, service disruption, or being leveraged in sophisticated supply chain attacks.
## Exploitation
- Status: Potential risk realized; article suggests exploitation is possible and SentinelOne found thousands of instances.
- Complexity: Low to Medium (Registration of a domain/service slot required, but fingerprinting the existing dangling record is straightforward).
- Attack Vector: Network (DNS query/HTTP access to the hijacked subdomain)
## Impact
- Confidentiality: High (If email forwarding or sensitive application data is accessible via the hijacked domain).
- Integrity: High (Ability to serve malicious content, deface websites, or pose as trusted entity).
- Availability: Medium (Service disruption possible if resources are inaccessible or traffic is redirected).
## Remediation
### Patches
- Not applicable (This is a configuration/operational flaw, not a software defect requiring a patch).
### Workarounds
1. **Update DNS Records:** Immediately remove or update any DNS records (CNAME, A, NS, MX) that point to deprovisioned, expired, or unused third-party or cloud resources.
2. **Audit SaaS Subscriptions:** Ensure that any services using subdomains (e.g., help desks, job boards) are actively managed, and their associated CNAME records are removed when services are terminated or trials expire.
3. **Cloud Resource De-provisioning:** When deleting cloud resources (like S3 buckets, load balancers), ensure corresponding DNS records are cleaned up simultaneously.
## Detection
- **Indicators of Compromise (IoC):** Observing unexpected content served from previously legitimate subdomains, or DNS lookups returning records pointing to unknown/uncontrolled external services.
- **Detection Methods and Tools:**
* Utilizing scanning tools (like those mentioned or commercial solutions like SentinelOne's Singularity Cloud Security) to actively hunt for "Dangling DNS" by resolving records and checking if the target resource still exists (e.g., checking for specific error messages like AWS S3 "NoSuchBucket").
* Prioritizing findings based on exploitability using offensive security engines that simulate subdomain takeover steps.
## References
- SentinelOne Blog concerning TJ-Actions (for context on runtime threats)
- SentinelOne Blog concerning XZ Utility (for context on supply chain threats)
- SentinelOne Blog concerning Log4j (for context on critical vulnerabilities)
- Real-world bug bounty case on Zendesk hijacking: hXXps://0xprial.com/the-art-of-zendesk-hijacking/
- SentinelOne KB for manual search and AWS remediation steps: hXXps://cloud-kb.sentinelone.com/public-subdomain-takeover-missing-origin-s3-bucket