CVE-2026-3833
Description
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.
Statement
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
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.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.5 | 7.4 | 6.5 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | Low | High | Low |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | Low | High | Low |
| Integrity Impact | Low | High | Low |
| Availability Impact | None | None | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
NVD: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
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