CVE-2020-1971

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 GENERAL_NAME_cmp which compares different instances of
a GENERAL_NAME to see if they are equal or not. This function behaves
incorrectly when both GENERAL_NAMEs contain an EDIPARTYNAME. A NULL pointer
dereference and a crash may occur leading to a possible denial of service
attack. OpenSSL itself uses the GENERAL_NAME_cmp 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 TS_RESP_verify_response and
   TS_RESP_verify_token) 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 s_server, s_client and verify tools have support for
   the “-crl_download” 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).

Notes