Dasher.A is a worm that exploits a vulnerability in Microsoft Windows Distributed Transaction Coordinator (MS05-051).
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The worm's dropper is a self-extracing RAR archive which drops the following files:
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:
The worm may also create the following files:
These files are used in exploiting.
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: