Dasher.B, W32/Dasher.B


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


Automatic action

Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

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Technical Details

Installation to system

The worm's dropper installs the following files:

  • %sysdir%\wins\SqlExp.exe%sysdir%\wins\SqlScan.exe%sysdir%\wins\svchost.exe

The file svchost.exe is the actual worm main file. SqlScan.exe is a port scan utilty and SqlExp.exe is a component that is used in MSDTC exploiting.

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 server instructs the infected system to download and execute the worm's dropper and keylogger.

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


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