Rule:

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Sid: 2100

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Summary:
Subseven 2.1 Gold is a Trojan Horse offering complete control of the 
infected host.

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Impact:
Possible theft of data and control of the targeted machine leading to a 
compromise of all resources the machine is connected to. This Trojan 
also has the ability to delete data, steal passwords and disable the 
machine. Other versions are capable of launching DDoS attacks.

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Detailed Information:
This Trojan affects the following operating systems:

	Windows 95
	Windows 98
	Windows ME

No other systems are affected. This is a windows executable that makes 
changes to the system registry, Win.ini and System.ini. When first 
executed the Trojan listens on either port 27374 or port 1243.

Subseven is an improved version of the Netbus Trojan (see sids 114, 
115), Subseven 2.1 Gold is an improved version of Subseven that 
affects Windows 95 and 98 implementations.

The Trojan changes system startup files and registry settings to add the
Subseven server to programs normally started on boot.

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Attack Scenarios:
This Trojan may be delivered to the target in a number of ways. This 
compromise can be in the form of a Win32 installation program that may 
use the extension ".jpg" or ".bmp" when delivered via e-mail for 
example.

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Ease of Attack:
This is Trojan activity, the target machine may already be compromised. 

Updated virus definition files are essential in detecting this Trojan.

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False Positives:
None Known

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False Negatives:
None Known

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Corrective Action:

This is a particularly difficult Trojan to remove and should only be 
attempted by an experienced Windows Administrator.

Edit the system registry to remove the extra keys or restore a 
previously known good copy of the registry.

Affected registry keys are:

  HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices

Registry key added:

	Winloader

Also affected:

	HKEY_CLASSES_ROOT\exefile\shell\open\command

This registry key should be blank, i.e. ""

The registry should also be searched for the entry  

  HKEY_CLASSES_ROOT\.dl 

if this exists it should be deleted.

This Trojan may also be started from the files win.ini and system.ini, 
remove the entry run=MSREXE.exe and change the line 
shell=Explorer.exe MSREXE.exe to the default value shell=explorer.exe.

Removal of the Trojan is also required, look for the file "MSREXE.exe" 
in the <drive>:\Windows\ or <drive>:\Windows\System\ folders.

Additionally, the files "RUN.EXE", "WINDOS.EXE" or "MUEEXE.EXE" may also
be present on the system and should be removed along with any references
to them in the start up locations in the same manner as for MSREXE.exe.

Note, these file names are the default ones and can be changed by the 
attacker.

A machine reboot is required to clear the existing process from running 
in memory.

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Contributors:
Sourcefire Research Team
Brian Caswell <bmc@sourcefire.com>
Nigel Houghton <nigel.houghton@sourcefire.com>

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Additional References:

Hackfix
http://www.hackfix.org/subseven/

McAfee
http://vil.mcafee.com/dispVirus.asp?virus_k=10566

Dark-e:
http://www.dark-e.com/archive/trojans/subseven/gold/index.shtml

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