GHSA-pwjx-qhcg-rvj4: webpki: CRLs not considered authoritative by Distribution Point due to faulty matching logic

If a certificate had more than one distributionPoint, then only the first distributionPoint would be considered against each CRL’s IssuingDistributionPoint distributionPoint, and then the certificate’s subsequent distributionPoints would be ignored.

The impact was that correct provided CRLs would not be consulted to check revocation. With UnknownStatusPolicy::Deny (the default) this would lead to incorrect but safe Error::UnknownRevocationStatus. With UnknownStatusPolicy::Allow this would lead to inappropriate acceptance of revoked certificates.

This vulnerability is thought to be of limited impact. This is because both the certificate and CRL are signed – an attacker would need to compromise a trusted issuing authority to trigger this bug. An attacker with such capabilities could likely bypass revocation checking through other more impactful means (such as publishing a valid, empty CRL.)

More likely, this bug would be latent in normal use, and an attacker could leverage faulty revocation checking to continue using a revoked credential.