nbd-server.c in Network Block Device (nbd-server) 2.9.21 allows remote attackers to cause a denial of service (NULL pointer dereference and crash) by causing a negotiation failure, as demonstrated by specifying a name for a non-existent export.
https://exchange.xforce.ibmcloud.com/vulnerabilities/67502
http://www.securityfocus.com/bid/47884
http://www.openwall.com/lists/oss-security/2011/05/17/1