A new Nirbot variant has been discovered that attempts to exploit the recent zero day vulnerability in Microsoft’s DNS Server Service (CVE-2007-1748).

Vulnerability to Worm Timeline:

• April 7 – This vulnerability was first reported by SANS in what was believed to be a targeted attack
• April 12 – Microsoft posted Microsoft Security Advisory (935964)
• April 14 – An exploit was made public
• April 15 – Three other exploits were made public
• April 15 – The first worm was submitted to McAfee Avert Labs late in the day

Analysis is on going. More details will be posted here.

Update April 16, 20:30 PDT
A second variant has been discovered.

First Variant
File Name: mdnex.exe (writes c:\U.exe)
File Size: 199,680 bytes
MD5: 0xc1a6a22b2415ba608fb894b4e036e19c

Second Variant
File Name: mozila.exe (writes c:\U.exe)
File Size: 270,848 bytes
MD5: 0×8f6cb8d895e60387fe3e41377d0f0d3f