F-Secure Trojan Information Pages: IRCBot.ST

[Summary] | [Disinfection] | [Detailed Description] | [Detection]

Name:

IRCBot.ST

Alias:

W32.Wargbot, IRC-Mocbot!MS06-040, W32/Cuebot-L, Backdoor.Win32.IRCBot.st, WORM_IRCBOT.JL

9609

Worm, Backdoor

Trojan

Win32

August 13, 2006

Summary

IRCBot.ST (also known as Mocbot) is the first variant of this IRC backdoor-worm to use the recently discovered MS06-040 exploit to spread itself. After being run, the backdoor installs itself to the system, modifies several security settings, attempts to connect to a remote IRC server, and starts listening for commands from a remote hacker.

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Disinfection

Automatic Disinfection

Usually standalone malware (backdoors, worms, trojans, etc.) is automatically removed by F-Secure Anti-Virus (FSAV) starting from version 5.40. Malware files get automatically renamed by FSAV, so they can not be started any more. In some rare cases, when automatic disinfection is not possible, a user can select disinfection action by him/herself to make FSAV rename or delete an infected file. In some special cases it is recommended to use specific disinfection tools provided by F-Secure. They can be downloaded from our ftp site:

ftp://ftp.f-secure.com/anti-virus/tools/

F-Secure Anti-Virus can be purchased from our webshop or from our authorised distributors. A trial version F-Secure Anti-Virus, limited to 30 days, can be downloaded from our website:

http://www.f-secure.com/download-purchase/

All the latest versions of FSAV can download anti-virus database updates automatically. However, these updates can be also downloaded and installed manually from our web or ftp sites:

http://www.f-secure.com/download-purchase/updates.shtml

Manual Disinfection

To manually disinfect standalone malware (backdoors, worms, trojans, etc.) it's usually enough to delete all infected files from a computer and to restart it. Active malware files are usually locked by operating system so different disinfection approaches are required for different operating systems.
Please note that manual disinfection is a risky process, so it is recommended only for advanced users.

If Windows 95, 98 and ME operating system is used, it is recommended to restart a computer from a bootable system diskette and to delete an infected file from command prompt. For example if a malicious file named ABC.EXE is located in Windows folder, it is usually enough to type the following command at command prompt:

DEL C:\WINDOWS\ABC.EXE

and to press Enter. After that an infected file will be gone. If Windows NT, 2000 or XP is used, a malicious file has to be renamed with a different extension (for example .VIR) and then a system has to be restarted. After restart a renamed malicious file will no longer be active and it can be easily deleted manually.

Malware Disinfection Tools

F-Secure provides disinfection tools for certain malware. These tools can be downloaded from this webpage:

http://www.f-secure.com/download-purchase/tools.shtml

ftp://ftp.f-secure.com/anti-virus/tools/

Windows System Restore Issues

If Windows ME or XP is used, it is recommended to disable System Restore feature of these operating systems to prevent a computer from re-infection by an already removed malware. The fact is that System Restore feature of these operating systems might save an infected file into the special folder and copy it back to a hard drive it every time it's been renamed or deleted by F-Secure Anti-Virus or by a user. Instructions on how to disable System Restore feature are here:

Windows ME:
http://www.f-secure.com/v-descs/sfc_dis.shtml

Windows XP:
http://www.f-secure.com/v-descs/sfc_dis1.shtml

It is recommended to re-enable System Restore after disinfection in order to restore stable system configuration in the future, if any crash or incompatibility issue occurs.

Failed Disinfection

In some cases F-Secure Anti-Virus might not disinfect a system automatically. In this case please visit our Support pages:

http://support.f-secure.com/enu/home/virusproblem/howtoclean/

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Detailed Description

The backdoor's file is a Windows PE executable, 9609 bytes long, packed with MEW file compressor and patched with PE_Patch. The backdoor's code has an additional encryption layer (simple XOR).

After the backdoor's file is run, it creates a mutex with the name "wgareg". This is done to prevent running more than one copy of the backdoor on the system. The backdoor also checks for the service with the name "wgareg" and if it's active, it skips the installation phase. During its startup phase, the backdoor creates a thread that checks for active debuggers and terminates the backdoor's process if a debugger is detected. Just before exiting, the backdoor encrypts its code with the same subroutine it used to decrypt at startup.

During the installation phase, the backdoor copies its file to the Windows System folder (usually named C:\Windows\System32\ by default) with the wgareg.exe name and then creates a service for that file with the following name and description:

Windows Genuine Advantage Registration Service
Ensures that your copy of Microsoft Windows is genuine and registered. Stopping or disabling this service will result in system instability.

Then the backdoor changes several settings in the Registry including those, related to Windows Security Center and Firewall. The following key values are set:

[HKEY_LOCAL_MACHINE\software\microsoft\ole]
"enabledcom"
[HKEY_LOCAL_MACHINE\system\currentcontrolset\control\lsa]
"restrictanonymous"
"restrictanonymoussam"
[HKEY_LOCAL_MACHINE\system\currentcontrolset\services
\lanmanserver\parameters]
"autoshareserver"
[HKEY_LOCAL_MACHINE\software\microsoft\security center]
"antivirusdisablenotify"
"antivirusoverride"
"firewalldisablenotify"
"firewalldisableoverride"
[HKEY_LOCAL_MACHINE\software\policies\microsoft\windowsfirewall
\domainprofile]
"enablefirewall"
[HKEY_LOCAL_MACHINE\software\policies\microsoft\windowsfirewall
\standardprofile]
"enablefirewall"

Once active the backdoor attempts to connect to one of the following remote IRC servers on TCP port 18067:

bniu.househot.com
ypgw.wallloan.com

The backdoor generates a random nickname and joins a password-protected channel, #n1, and waits for commands from a channel operator. A remote hacker who is controlling the backdoor can do any of the following:

Start any files located on the remote (infected) computer
Update the backdoor's file from the Internet
Disable and uninstall the backdoor
Find files on the remote (infected) computer
Create a remote command shell
Flush the DNS cache
Send commands to an AIM (AOL Instant Messenger) window
Connect to a different IRC server
Create a simple proxy
Perform an SYN flood
Perform a DDoS (Distributed Denial of Service) attack
Spread to vulnerable computers using the MS06-040 exploit

The backdoor uses the recently discovered MS06-040 exploit to spread to remote computers. When a hacker initiates a scan within a defined range of IP addresses, the backdoor attempts to connect to the selected IP addresses and deliver the exploit to those computers. If a remote computer is vulnerable, then it becomes infected with the backdoor.

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Detection

F-Secure Anti-Virus detects this malware with the following updates:

[FSAV_Database_Version]

Version = 2006-08-13_01.

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F-Secure Corporation

THIS VIRUS IS RANKED AS LEVEL2 ALERT UNDER
F-SECURE RADAR.

Radar Alert LEVEL2

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