Vulnerability details

Improper certificate validation in the directoryName name-constraint check (PkixNameConstraintValidator.WithinDNSubtree) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows an attacker who controls, or can have certificates issued by, a name-constrained intermediate CA to get certificates accepted by PKIX path validation whose subject distinguished name, or a directoryName subjectAltName, lies outside the CA's permitted subtrees, via a name that places other RDNs ahead of a copy of the permitted RDN sequence, because the check looks for the constraint's first RDN anywhere in the name and compares the remaining RDNs from that position, instead of requiring the constraint to be an initial prefix of the name as RFC 5280 sections 4.2.1.10 and 7.1 require.

• https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63577 vendor-advisory
• https://github.com/bcgit/bc-csharp/commit/606e9153b97a265c70ca8293d21ec859344d7de8 patch
• https://github.com/bcgit/bc-csharp/commit/75c3c576602886180ed92a63c89419e3bd63b392 patch