Bobax is a new, Sasser-like trojan proxy that uses the MS04-011 (LSASS.EXE) vulnerability to propagate. When instructed to do so it scans random IP addresses for vulnerable computers.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
The Bobax executable is packed with a modified version of UPX.
The strings within its body are encoded using a simple scrambling function.
It opens a HTTP server on the infected machine, to further distribute itself upon infection of new hosts.
When attempting to find new targets, it will probe the port 5000 ( Universal Plug and Play (UPnP) ) , a sign of a machine running Windows XP. If found, it will attempt infection of the target by means of using the LSASS exploit made famous by the Sasser worm.
When Bobax infects a host, the exploit uses HTTP to download the executable from a webserver which listens on a random port on the attacker host. The data is downloaded into a dropper file called 'svc.exe'.
The dropper drops a DLL to the temporary directory with a random name. The DLL is launched by injecting it to Explorer with a technique called DLL Injection. Because the code runs as a thread in Explorer it's not visible as a separate process.
Detection for this malware was published on May 16th, 2004 in the following F-Secure
Detection Type: PC
Description Created: Gergely Erdelyi & Ero Carrera, May 16th, 2004;