Threat Description

Dasher.A

Details

Aliases:Dasher.A, W32/Dasher.A
Category:Worm
Type:
Platform:W32

Summary



Dasher.A is a worm that exploits a vulnerability in Microsoft Windows Distributed Transaction Coordinator (MS05-051).



Removal


Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.

More

You may wish to refer to the Support Community for further assistance. You also may also refer to General Removal Instructions for a general guide on alternative disinfection actions.



Technical Details



Installation to system

The worm's dropper is a self-extracing RAR archive which drops the following files:

  • %windir%\Temp\SqlExp.exe
  • %windir%\Temp\Sqlrep.exe
  • %windir%\Temp\SqlScan.exe
  • %windir%\Temp\Sqltob.exe

The file Sqltob.exe is the actual worm main file. Sqlrep.exe is utilty called "Replace Commander". SqlScan.exe is a port scan utilty and SqlExp.exe is a component that is used in MSDTC exploiting.

When the main file is run, it adds the following registry entry to ensure that it is started when a user logs on or the system is restarted:

  • [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run] "Windows Update" = "%windir%\Temp\Sqltob.exe"

The worm may also create the following files:

  • %windir%\Temp\Result.txt
  • %windir%\Temp\SqlScan.bat

These files are used in exploiting.

Spreading using MSTDC vulnerability

The worm scans for systems vulnerable to MSTDC (MS05-051) through TCP/1025. It constructs random addresses using a fixed list of A-class networks. If it finds a system responding to TCP SYN scan, it sends the exploit payload. The payload connects to remote address and waits for instructions. At the time of this writing, the remote server is not accessible. According to reports, the server may instruct the infected system to download and activate the worm's dropper.

Please see the following page for detailed information on the vulnerability:

http://www.microsoft.com/technet/security/Bulletin/MS05-051.mspx



Detection


Dasher.A is detected with the following F-Secure Anti-Virus updates:
Detection Type: PC
Database: 2005-12-15_03



Description Created: Jarkko Turkulainen
Technical Details: Jarkko Turkulainen, December 15, 2005
Description Last Modified: Jarkko Turkulainen, December 15, 2005


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