The compare_dn function in utils/identification.c in strongSwan 4.3.3 through 5.1.1 allows (1) remote attackers to cause a denial of service (out-of-bounds read, NULL pointer dereference, and daemon crash) or (2) remote authenticated users to impersonate arbitrary users and bypass access restrictions via a crafted ID_DER_ASN1_DN ID, related to an "insufficient length check" during identity comparison.
Debian Linux Security Advisory 2789-1 - A vulnerability has been found in the ASN.1 parser of strongSwan, an IKE daemon used to establish IPsec protected links.