Summary

Mitglieder.H is a descendant of the Mitglieder trojan family with the ability to spread to computers infected with the Mydoom.A worm.

The main payload of the worm is a backdoor / SMTP proxy that listens on TCP port 35555. The payload includes other parts like disabling antivirus software and reporting of infected computers.

Additional Details

System Infection

When run, the worm copies itself as SYSTEM.EXE to the Windows System directory and creates the following entry in the System Registry:

[HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run] "ssgrate.exe" = "%winsysdir%\system.exe"
where %winsysdir% is the name of Windows System directory.

It also creates another key in the Registry where it stores its internal variables:

[HKCU\SOFTWARE\DateTime]
Network Propagation

To spread Mitglieder.H scans random IP addresses for open TCP port 3127. Exploiting the backdoor installed by Mydoom.A it copies itself to those hosts.

Backdoor and SMTP proxy

The main component of the payload is a TCP backdoor / SMTP proxy that listens on port 35555. Through the backdoor a remote attacker can instruct the infected computer to build up a TCP connection and relay the traffic.

The backdoor component uses a list of URLs to PHP files where it reports the address of the infected computer along with the port number where the backdoor is sitting.

Disabling Security Software

The payload of Mitglieder.H contains a thread that terminates processes with the following names:

ATUPDATER.EXE AVWUPD32.EXE AVPUPD.EXE LUALL.EXE DRWEBUPW.EXE ICSSUPPNT.EXE ICSUPP95.EXE UPDATE.EXE NUPGRADE.EXE ATUPDATER.EXE AUPDATE.EXE AUTODOWN.EXE AUTOTRACE.EXE AUTOUPDATE.EXE AVXQUAR.EXE CFIAUDIT.EXE MCUPDATE.EXE NUPGRADE.EXE SMS.EXE OUTPOST.EXE
Remote Update

The worm contains several HTTP links that is uses to download and execute programs. At this moment the links are inaccessible so the worm will not download anything.

Detection

Detection in F-Secure Anti-Virus was published on February 12th, 2004 in update:

[FSAV_Database_Version]
Version=2004-02-12_02

Technical Details: Gergely Erdelyi and Alexey Podrezov; February 12th, 2004;