Summary

This Korgo (aka Padobot) variant was found in the beginning of June, 2004. It is very similar to the previous 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 10752 bytes long packed with UPX file compressor. The unpacked file's size is about 18 kilobytes.

When the worm's file is run, it first deletes the FTPUPD.EXE file. Then the worm creates a mutex with the "uterm11" 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 Disk Defragmenter System Restore Service Bot Loader SysTray WinUpdate Windows Update Service avserve.exe avserve2.exeUpdate Service
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] "Windows Update" = "%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 'jsoxse.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. It also listens on TCP port 3067. Through this port the worm can download files to Windows System folder and run them. However, before that a secure authentication takes place so unauthorised clients are not allowed to upload and run files. Additionally the worm can listen on random TCP ports.

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 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 #taty channel and creates a bot with a random name there.

Detection

Generic detection of Korgo.H was published on June 3rd, 2004 in the following F-Secure Anti-Virus update:

[FSAV_Database_Version]
Version=2004-06-03_01

Technical Details: Alexey Podrezov; June 8th, 2004;