# CVE-2026-67693: GnuTLS improper X.509 certificate validation

Source: https://junglewise.ai/threats/cve-2026-67693-an-issue-in-gnutls-v-3-8-13-allows-an-attacker-to-obtain  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-08. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-67693 · Severity: high · CVSS 7.5 · Published 2026-10-08

GnuTLS is a cryptographic library used to secure communications over TLS/SSL. The library fails to properly validate X.509 certificates that contain conflicting key usage restrictions, allowing an attacker to forge or misuse certificates that should be rejected. This could enable unauthorized TLS connections, impersonation attacks, or bypass of certificate-based security policies in applications relying on strict key usage enforcement.

Technologies: [GnuTLS](https://junglewise.ai/threats/technologies/gnutls-gnutls). Vendors: [GnuTLS](https://junglewise.ai/threats/vendors/gnutls).

## Quick answers

**Is CVE-2026-67693 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-67693 being exploited in the wild.

**How severe is CVE-2026-67693?** High severity, with a CVSS score of 7.5, published 8 October 2026.

**Which products and versions are affected?** GnuTLS 3.8.13.

**Is there a fix for CVE-2026-67693?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-67693 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-67693?** Check whether you run GnuTLS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

GnuTLS 3.8.13 treats a Key Usage extension with all bits set to zero as if the extension were absent, and does not cross-check Key Usage bits when verifying Extended Key Usage purposes. An end-entity certificate with critical Key Usage cleared but Extended Key Usage containing id-kp-serverAuth is incorrectly accepted by both certtool and gnutls-cli, violating RFC 5280. The vulnerability requires a malicious or compromised certificate authority and affects deployments that rely on Key Usage policy enforcement.

## Affected products

- GnuTLS GnuTLS 3.8.13

## Timeline

- 2025-01: other: Issue reported upstream as #1642 but remained open without fix
- 2026-09-03: disclosed: Public disclosure via GitHub gist
- 2026-10-08: advisory

## References

- [http://gnutls.com/](http://gnutls.com/)
- [https://gist.github.com/lkloliver/6fbfc191bc6163942c8017551ac3f238](https://gist.github.com/lkloliver/6fbfc191bc6163942c8017551ac3f238)

## Related threats

- [GnuTLS certificate validation denial of service](https://junglewise.ai/threats/cve-2026-95209-an-issue-in-gnutls-v3-8-13-causes-legitimate-ca-certificates-to)
- [GnuTLS improper certificate validation in extension processing](https://junglewise.ai/threats/cve-2026-95210-improper-certificate-validation-in-gnutls-v3-8-13-causes-the)