VU#573195: Go, OpenSSL, Apple, LibreSSL, pyca, wolfSSL Name-Constraint Inconsistency in RFC 5280 Implementation

Summary

Overview This note covers differences in how TLS libraries interpret X.509 Name Constraints. A certificate that one library accepts may be rejected by another. Some of those differences are defects; others follow from behavior that RFC 5280 does not fully specify. Description The observed differences concern DNS name comparison, IP address handling, URI-authority parsing, and wildcard matching. These include both implementation defects and behavior not fully specified by RFC 5280. DNS-name comparison. RFC 5280 requires case-insensitive matching for DNS names. GnuTLS compared some names' case-sensitivity at the time of reporting (CVE-2026-3833, later fixed in 3.8.13). A distinct Go report concerns case handling in wildcard parent-constraint lookup, not ordinary hostname comparison. IP address handling. RFC 5280 defines separate IPv4 and... Related CVEs: CVE-2026-34073, CVE-2026-3833.

Why it matters

CERT/CC notes often cover coordinated disclosures, multi-vendor exposure, infrastructure risk, or cases where remediation guidance is still developing.

Operator check

Review the CERT/CC Vulnerability Note and compare the affected vendor and product list against your inventory. Apply vendor fixes or compensating controls for 5280 Implementation where available.

Sources