The pkinit_check_kdc_pkid function in plugins/preauth/pkinit/pkinit_crypto_openssl.c in the PKINIT implementation in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.10.4 and 1.11.x before 1.11.1 does not properly handle errors during extraction of fields from an X.509 certificate, which allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a malformed KRB5_PADATA_PK_AS_REQ AS-REQ request.