There is an issue similar to the one fixed with the previous commit when
using directoryName (DN) name constraints. Some RDNs have to be matched
in a case-insensitive manner, which we e.g. do in
`identification.c::rdn_equals`. By not doing it for name constraints,
a malicious intermediate CA could evade an excluded name constraint
just by modifying the case in such an RDN.
While we could use the mentioned function in `dn_matches`, this doesn't
properly fix the problem because the function is basically too strict.
Especially in regards to RDNs of type UTF8String, which are only compared
binary. To match these properly, we'd have to implement the string
preparation described in RFC 5280, section 7.1 and the referenced RFCs.
Until that's the case, we reject excluded name constraints of type
directoryName as we are unable to enforce them.
Fixes: a2b340764f ("Implemented NameConstraint matching in constraints plugin")
Fixes: CVE-2026-35331
Tobias Brunner
64130ede5c