CVE-2020-1971: EDIPARTYNAME NULL pointer dereference

As per upstream advisory:

The X.509 GeneralName type is a generic type for representing different types of names. One of those name types is known as EDIPartyName. OpenSSL provides a function GENERALNAMEcmp which compares different instances of a GENERALNAME to see if they are equal or not. This function behaves incorrectly when both GENERALNAMEs contain an EDIPARTYNAME. A NULL pointer dereference and a crash may occur leading to a possible denial of service attack.

OpenSSL itself uses the GENERALNAMEcmp function for two purposes:

1. Comparing CRL distribution point names between an available CRL and a CRL distribution point embedded in an X509 certificate 2. When verifying that a timestamp response token signer matches the timestamp authority name (exposed via the API functions TSRESPverifyresponse and TSRESPverifytoken)

If an attacker can control both items being compared then that attacker could trigger a crash. For example if the attacker can trick a client or server into checking a malicious certificate against a malicious CRL then this may occur. Note that some applications automatically download CRLs based on a URL embedded in a certificate. This checking happens prior to the signatures on the certificate and CRL being verified. OpenSSL's sserver, sclient and verify tools have support for the "-crldownload" option which implements automatic CRL downloading and this attack has been demonstrated to work against those tools.

— Red Hat

OpenSSL is vulnerable to a denial of service, caused by a NULL pointer dereference. If the GENERALNAMEcmp function contain an EDIPARTYNAME, an attacker could exploit this vulnerability to cause the application to crash.

— IBM

The X.509 GeneralName type is a generic type for representing different types of names. One of those name types is known as EDIPartyName. OpenSSL provides a function GENERALNAMEcmp which compares different instances of a GENERALNAME to see if they are equal or not. This function behaves incorrectly when both GENERALNAMEs contain an EDIPARTYNAME. A NULL pointer dereference and a crash may occur leading to a possible denial of service attack. OpenSSL itself uses the GENERALNAMEcmp function for two purposes: 1) Comparing CRL distribution point names between an available CRL and a CRL distribution point embedded in an X509 certificate 2) When verifying that a timestamp response token signer matches the timestamp authority name (exposed via the API functions TSRESPverifyresponse and TSRESPverifytoken) If an attacker can control both items being compared then that attacker could trigger a crash. For example if the attacker can trick a client or server into checking a malicious certificate against a malicious CRL then this may occur. Note that some applications automatically download CRLs based on a URL embedded in a certificate. This checking happens prior to the signatures on the certificate and CRL being verified. OpenSSL's sserver, sclient and verify tools have support for the "-crldownload" option which implements automatic CRL downloading and this attack has been demonstrated to work against those tools. Note that an unrelated bug means that affected versions of OpenSSL cannot parse or construct correct encodings of EDIPARTYNAME. However it is possible to construct a malformed EDIPARTYNAME that OpenSSL's parser will accept and hence trigger this attack. All OpenSSL 1.1.1 and 1.0.2 versions are affected by this issue. Other OpenSSL releases are out of support and have not been checked. Fixed in OpenSSL 1.1.1i (Affected 1.1.1-1.1.1h). Fixed in OpenSSL 1.0.2x (Affected 1.0.2-1.0.2w).