GEN:SID 1:2336
Message TFTP NULL command attempt
Summary This event is generated when an attempt is made to exploit a known
vulnerability in a Verilink NetEngine Broadband Router.
Impact Denial of Service (DoS)
Detailed Information TFTP is used to transfer files between hosts and devices. This event is indicative of spurious
activity in TFTP traffic between hosts.

It is possible for an attacker to send a NULL opcode to a Verilink
NetEngine Broadband Router, this may cause the router to become
unresponsive.
Affected Systems Verilink NetEngine 6100-4
Attack Scenarios An attacker may use a publicly available exploit script to cause the
DoS.
Ease of Attack Simple. Exploit code is available.
Corrective Action Apply the appropriate vendor supplied patches.

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