Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-04-30T17:26:28 gnutls: GnuTLS: Policy bypass due to case-sensitive nameConstraints comparison 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N CWE-178

A flaw was found in gnutls. This vulnerability occurs because gnutls performs case-sensitive comparisons of `nameConstraints` labels, specifically for `dNSName` (DNS) or `rfc822Name` (email) constraints within `excludedSubtrees` or `permittedSubtrees`. A remote attacker can exploit this by crafting a leaf certificate with casing differences in the Subject Alternative Name (SAN), leading to a policy bypass where a certificate that should be rejected is instead accepted. This could result in unauthorized access or information disclosure.

A flaw was found in gnutls. This vulnerability occurs because gnutls performs case-sensitive comparisons of `nameConstraints` labels, specifically for `dNSName` (DNS) or `rfc822Name` (email) constraints within `excludedSubtrees` or `permittedSubtrees`. A remote attacker can exploit this by crafting a leaf certificate with casing differences in the Subject Alternative Name (SAN), leading to a policy bypass where a certificate that should be rejected is instead accepted. This could result in unauthorized access or information disclosure.

This issue is particularly important because it affects the correct enforcement of X.509 nameConstraints, which are specifically designed to limit the authority of subordinate CAs. In GnuTLS, the use of case-sensitive comparisons (memcmp) for dNSName and the domain portion of rfc822Name violates the case-insensitive matching requirements defined in RFC 5280 and RFC 4343. As a result, a constrained subordinate CA can bypass excludedSubtrees or permittedSubtrees restrictions simply by changing the letter casing of a domain in the SAN (e.g., ExAmPlE.CoM vs example.com). Since nameConstraints are often the only mechanism enforcing domain boundaries in delegated PKI hierarchies, this flaw effectively allows a malicious or compromised sub-CA to issue certificates for domains that should be cryptographically prohibited, enabling unauthorized certificate validation and potential TLS impersonation of restricted services. Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability. Red Hat Hardened Images 2026-05-02T00:00:00Z RHSA-2026:13274 gnutls-main-3.8.13-1.hum1 Red Hat Enterprise Linux 10 Affected gnutls Red Hat Enterprise Linux 6 Affected gnutls Red Hat Enterprise Linux 7 Affected gnutls Red Hat Enterprise Linux 8 Affected gnutls Red Hat Enterprise Linux 9 Affected gnutls Red Hat OpenShift Container Platform 4 Affected rhcos https://www.cve.org/CVERecord?id=CVE-2026-3833 https://nvd.nist.gov/vuln/detail/CVE-2026-3833 https://gitlab.com/gnutls/gnutls/-/issues/1803