The vulnerability CVE-2026-3833 in GnuTLS involves improper handling of case sensitivity when comparing nameConstraints labels, such as dNSName and rfc822Name, in certificate validation. Because GnuTLS performs case-sensitive comparisons in excludedSubtrees or permittedSubtrees, an attacker can craft a leaf certificate with different casing in the Subject Alternative Name to bypass policy checks. This results in acceptance of certificates that should be rejected, potentially enabling unauthorized access or information disclosure. Red Hat has issued updates for GnuTLS packages in Red Hat Enterprise Linux 8 and Red Hat Hardened Images to fix this issue.

The vulnerability allows a remote attacker to bypass certificate validation policies by exploiting case-sensitive comparisons in nameConstraints, potentially leading to unauthorized access or information disclosure. The CVSS v3.1 base score is 6.5 (medium severity), indicating a moderate impact with network attack vector, low complexity, no privileges required, no user interaction, and impacts on confidentiality and integrity but not availability.

Red Hat has released security updates for GnuTLS packages that fix this vulnerability. Users of Red Hat Hardened Images and Red Hat Enterprise Linux 8 should apply the available GnuTLS updates as detailed in Red Hat advisories RHSA-2026:13274 and RHSA-2026:20611. These updates address the case-sensitivity issue in nameConstraints comparison. Patch status is confirmed as fixed by Red Hat. Follow the vendor's official update procedures to remediate this vulnerability.