net-snmp: A malformed OID in a SET request to NET-SNMP-AGENT-MIB::nsLogTable can cause a NULL pointer dereference

net-snmp provides various tools relating to the Simple Network Management Protocol. Prior to version 5.9.2, a user with read-only credentials can use a malformed OID in a `GET-NEXT` to the `nsVacmAccessTable` to cause a NULL pointer dereference. Version 5.9.2 contains a patch. Users should use strong SNMPv3 credentials and avoid sharing the credentials. Those who must use SNMPv1 or SNMPv2c should use a complex community string and enhance the protection by restricting access to a given IP address range.