An issue in gnutls version 3.8.13 causes the library to fail to reject end‑entity X.509 certificates that contain contradictory Key Usage and Extended Key Usage fields. Because the certificate‑verification routine does not enforce the mutual consistency of these certificate extensions, an attacker could supply such a certificate during a TLS handshake and trick the library into accepting it. This flaw effectively bypasses the intended cryptographic restrictions and allows the attacker to intercept or read data that should be protected by the certificate.

The affected product is the gnutls library, specifically version 3.8.13. Systems that embed this library and perform standard X.509 certificate validation against end‑entity certificates are at risk. No other vendor products are listed in the advisory.

This vulnerability has no publicly available exploit at this time and is not listed in CISA’s KEV catalog. The EPSS score is 0.00198 (less than 1%) and the CVSS score is 3.7, indicating low to moderate severity. An attacker who can supply a malicious certificate—whether as a man‑in‑the‑middle or a rogue CA—could extract sensitive information or gain unauthorized access.