GEN:SID 1:2339
Message TFTP NULL command attempt
Summary This event is generated when an attempt is made to exploit a known
vulnerability in Verilink Netengine Broadband Routers.
Impact Denial of Service (DoS)
Detailed Information TFTP is used to transfer files between hosts. This event is indicative of spurious
activity in TFTP traffic from a host to a router.

It is possible for an attacker to expoit a DoS condition in
Netengine routers. If a UDP packet containing a double-null opcode is
sent to the router's TFTP port the router may crash, thus causing the
DoS.
Affected Systems Verilink Netengine Broadband Routers
Attack Scenarios An attacker may use a publicly available exploit script to take
advantage of the vulnerability.
Ease of Attack Simple. Exploit code exists.
Corrective Action Apply the appropriate vendor supplied patches.

Upgrade to the latest non-affected version of the software.
Additional References  
Rule References bugtraq: 7575