The vulnerability CVE-2026-3833 in gnutls is caused by case-sensitive comparisons of nameConstraints labels (dNSName or rfc822Name) in excludedSubtrees or permittedSubtrees. This improper handling allows a remote attacker to present a leaf certificate with differently cased SAN entries to bypass policy enforcement, resulting in acceptance of certificates that should be rejected. Red Hat has released security updates for gnutls in Red Hat Enterprise Linux 7 Extended Lifecycle Support to address this issue, among other related certificate validation flaws. The vulnerability has a CVSS 3.1 base score indicating moderate severity with confidentiality and integrity impacts but no availability impact. No known exploits in the wild have been reported. The vendor advisory provides detailed patch information and instructions for remediation.

Successful exploitation allows an attacker to bypass certificate validation policies by exploiting case-sensitive comparisons in nameConstraints, potentially leading to unauthorized access or information disclosure. The CVSS vector indicates that the attack can be performed remotely over the network without privileges or user interaction, impacting confidentiality and integrity. There is no known exploitation in the wild at this time.

Red Hat has released updated gnutls packages that fix this vulnerability. Users of Red Hat Enterprise Linux 7 Extended Lifecycle Support should apply the security updates as described in Red Hat advisory RHSA-2026:43575 and the related article https://access.redhat.com/articles/11258. Applying these official patches fully mitigates the vulnerability. No additional mitigation steps are required beyond applying the vendor-provided updates.