Summary

This Korgo (aka Padobot) variant was found in the very end of May, 2004. It is very similar to other Korgo variants. It spreads throughout the Internet using a vulnerability in Microsoft Windows LSASS. A description of the vulnerability can be found in Microsoft Security Bulletin MS04-011:

http://www.microsoft.com/technet/security/bulletin/MS04-011.mspx

Additional Details

The worm's file is a PE executable 9728 bytes long packed with UPX file compressor. The unpacked file's size is about 15.8 kilobytes.

When the worm's file is run, it first deletes the FTPUPD.EXE file. Then the worm creates a mutex with the "uterm8" name. This is done to avoid loading multiple copies of the worm into memory.

Next, the worm deletes Registry key values and terminates processes with any of the following names:

Windows Security Manager System Service Manager Bot Loader SysTray WinUpdate avserve.exe avserve2.exe
The key values are deleted from the following Registry key:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]
After that the worm installs itself to system and creates a startup key for its file in the Registry. The worm's file is copied to Windows System folder with a randomly generated name. The following Registry key is then created:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run] "System Restore Service" = "%WinSysDir%\<random>.exe"
where WinSysDir represents Windows System directory name and <random> represents random characters. The name of the worm's file can be for example 'jweisy.exe'.

Additionally the worm can create the following Registry key:

[HKLM\Software\Microsoft\Wireless] "Client" = "1"
The worm tries to start its spreading routine as a remote thread of Windows Explorer. If this fails, the worm starts the spreading thread directly.

Being active, the worm starts the IDENT server on TCP port 113. Additionally the worm can listen on random TCP ports. The worm doesn't listen on port 3067 like its previous variant, so it doesn't allow to upload and run files on an infected computer.

The worm spreads to remote computers using LSASS vulnerability. It contacts remote computers on TCP port 445, exploits the vulnerability and copies its file to a remote system.

The worm tries to contact the following IRC servers on port 6667:

moscow-advokat.ru gaz-prom.ru graz.at.eu.undernet.org flanders.be.eu.undernet.org caen.fr.eu.undernet.org brussels.be.eu.undernet.org los-angeles.ca.us.undernet.org washington.dc.us.undernet.org london.uk.eu.undernet.org irc.tsk.ru lia.zanet.net gaspode.zanet.org.za irc.kar.net
If connection is successful, the worm joins the #stalin channel and creates a bot with a random name there.

Detection

Korgo.F is detected generically with the updates that were published on May 26th, 2004. Database version:

[FSAV_Database_Version]
Version=2004-05-26_02

Exact detection of Korgo.F is available since the following FSAV updates:

[FSAV_Database_Version]
Version=2004-06-02_03

Technical Details: Alexey Podrezov; June 3rd, 2004;