Overview
CVE-2025-61727 is a certificate vulnerability that reveals a flaw in how excluded subdomain constraints are enforced when wildcard Subject Alternative Names (SANs) are present in leaf certificates. Specifically, the vulnerability allows a leaf certificate with a wildcard SAN to bypass an excluded subdomain constraint intended to limit its scope.
Published on 2025-12-03T20:16:25.607, this issue highlights the importance of rigorous certificate validation and the potential risks associated with misconfigured or improperly enforced certificate constraints.
Technical Details
The core of the vulnerability lies in the interpretation of certificate chain validation logic. When a certificate authority (CA) sets up constraints, it might exclude specific subdomains from being certified. For instance, a CA might exclude test.example.com. However, CVE-2025-61727 demonstrates that this exclusion is not properly enforced if the leaf certificate contains a wildcard SAN such as *.example.com.
In this scenario, a certificate claiming *.example.com would be considered valid, effectively bypassing the intended exclusion of test.example.com. This circumvention is due to the certificate validation process failing to properly reconcile the wildcard SAN with the specific subdomain exclusion.
CVSS Analysis
Currently, a CVSS score is not available (N/A) for CVE-2025-61727. Further analysis is required to determine the base score, temporal score, and environmental score to accurately reflect the risk associated with this vulnerability.
However, the potential impact could be significant, depending on the context in which certificates are used. A successful exploitation of this vulnerability could lead to unauthorized access, man-in-the-middle attacks, or other security breaches.
Possible Impact
The impact of CVE-2025-61727 can be considerable. An attacker could potentially:
- Obtain certificates covering subdomains that should have been excluded.
- Perform man-in-the-middle (MITM) attacks by impersonating services on the affected subdomains.
- Gain unauthorized access to sensitive data or systems.
- Compromise the overall security and trust of the affected domain.
Mitigation or Patch Steps
Mitigation steps depend on the affected system or library. The provided references point to a fix in the Go programming language. Here’s a general approach:
- Update the Go programming language: If your application uses Go, update to a version that includes the fix referenced in go.dev/cl/723900.
- Review Certificate Validation Logic: Examine and update your certificate validation logic to ensure that wildcard SANs are correctly handled in conjunction with excluded subdomain constraints. Specifically, verify that exclusions are applied even when a wildcard certificate is present.
- Monitor Certificate Issuance: Implement monitoring and alerting mechanisms to detect potentially malicious certificate issuances that exploit this vulnerability.
