Dasher.A

Classification

Worm

-

W32

Dasher.A, W32/Dasher.A

Summary

Dasher.A 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.

Suspect a file is incorrectly detected (a False Positive)?

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest detection database updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    NOTE If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note You need administrative rights to change the settings.

For more Support

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User Guide

See the user guide for your product on the Help Center.

Contact Support

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Submit a sample

Submit a file or URL for further analysis.

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:

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