Sinit

Threat description

Details

Summary

Sinit is a backdoor that opens a random UDP port and allows unauthorized access to infected machine. According to reports, this port can be used as a part of peer-to-peer network enabling uncentralized distribution of malware to infected computers.



Removal

Automatic action

Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.

More scanning & removal options

More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.

You may also refer to the Knowledge Base on the F-Secure Community site for more information.

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Technical Details

System installation

When run, the backdoor copies itself to the System directory as 'svcinit.exe'. It adds the following registry key to ensure it will be executed when the system is started:

[HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]  "Userinit" = "%System%\userinit.exe,%System%\svcinit.exe"   

If the system is running windows 9x (95, 98 or ME), it uses the following key instead:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices]  "SVC Service" = "%System%\svcinit.exe"   
Backdoor

Sinit opens two UDP ports, port 53 and a random port. Using these ports, the backdoor can receive updates and other programs. It should be noted that domain name protocol (DNS) also uses UDP port 53, but the protocol is completely different.

The backdoor also opens a TCP port 53 which acts as a simple HTTP server. When a HTTP GET request for 'ks.exe' or 'kx.htm' is received, the backdoor sends a copy of itself.

Detection

F-Secure Anti-Virus detects various variants of the Sinit backdoor starting with the following update:

Detection Type: PC

Database: 2003-04-25_01

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