In open62541 v1.5.5, the server-side AddReferences implementation contains an incomplete validation flaw for non-local ExpandedNodeId targets. A remote attacker can send a crafted AddReferencesRequest with an empty targetServerUri and a non-zero targetNodeId.serverIndex, causing the target node pointer to remain NULL while execution continues.
https://github.com/open62541/open62541/issues/8172
https://github.com/open62541/open62541/blob/v1.5.5/src/ua_types.c
https://github.com/open62541/open62541/blob/v1.5.5/src/server/ua_services_nodemanagement.c
https://github.com/open62541/open62541/blob/v1.5.5/include/open62541/types.h