VU#573195: Go, OpenSSL, Apple, LibreSSL, pyca, wolfSSL Name-Constraint Inconsistency in RFC 5280 Implementation
CERT/CC warns TLS libraries inconsistently enforce X.509 name constraints, with fixes for GnuTLS and pyca/cryptography.
CERT/CC VU#573195 describes inconsistent X.509 Name Constraints handling across Go crypto/x509, Apple Security.framework, OpenSSL, LibreSSL, pyca/cryptography, and wolfSSL. Differences cover DNS comparison, IPv4-mapped IPv6 addresses, URI-authority parsing, and wildcards; some are defects and others stem from gaps in RFC 5280. GnuTLS case-sensitivity issue CVE-2026-3833 was fixed in 3.8.13, and pyca/cryptography CVE-2026-34073, where constraints were not checked against the requested peer name, was fixed in 46.0.6. CERT/CC says an attacker would need a trusted signature and a relying application, and that disagreement alone does not show exploitation.