There is a type confusion vulnerability relating to X.400 address processing inside an X.509 GeneralName. X.400 addresses were parsed as an ASN1 STRING but the public structure definition for GENERAL NAME incorrectly specified the type of the x400Address field as ASN1 TYPE. This field is subsequently interpreted by the OpenSSL function GENERAL NAME cmp as an ASN1 TYPE rather than an ASN1 STRING. When CRL checking is enabled (i.e. the application sets the X509 V FLAG CRL CHECK flag), this vulnerability may allow an attacker to pass arbitrary pointers to a memcmp call, enabling them to read memory contents or enact a denial of service. In most cases, the attack requires the attacker to provide both the certificate chain and CRL, neither of which need to have a valid signature. If the attacker only controls one of these inputs, the other input must already contain an X.400 address as a CRL distribution point, which is uncommon. As such, this vulnerability is most likely to only affect applications which have implemented their own functionality for retrieving CRLs over a network.