GnuTLS SAN case-sensitivity flaw can bypass nameConstraints
CVE-2026-3833 Published on April 30, 2026
Gnutls: gnutls: policy bypass due to case-sensitive nameconstraints comparison
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.
Vulnerability Analysis
CVE-2026-3833 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. An automatable proof of concept (POC) exploit exists. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality and integrity, and no impact on availability.
Timeline
Reported to Red Hat.
Made public. 52 days later.
Weakness Type
Improper Handling of Case Sensitivity
The software does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results.
Products Associated with CVE-2026-3833
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