Backdoor.IRC.Ratsou

SUMMARY

Backdoor.IRC.Ratsou is a Backdoor Trojan that gives a hacker full control of your computer.

Protection

• Virus Definitions (LiveUpdate™ Weekly) May 7, 2003
• Virus Definitions (Intelligent Updater) May 5, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Medium
• Compromises Security Settings: Allows unauthorized remote access to an infected computer.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Backdoor.IRC.Ratsou may be downloaded by Trojan.Downloader.Aphe from the Web site, http:/ /amateur.freegayspace.com.

When Trojan.Downloader.Aphe runs, it may download a file as C:Roof.exe, which is also detected as Trojan.Downloader.Aphe, from a specific Web site. Then, the Trojan executes C:Roof.exe.

C:Roof.exe downloads a third file as C:Newconf.exe, which is detected as Backdoor.IRC.Ratsou, from the same Web site. Then, the Trojan executes C:Newconf.exe.

When C:Newconf.exe runs, it does the following:

1. Creates the folder, %Windir%HelpTours.
   
   NOTE: %Windir% is a variable. The Trojan locates the Windows installation folder (by default, this is C:Windows or C:Winnt) and copies itself to that location.
   
   
2. Creates the following files in the Windows installation folder:
   • AIM.TXT, which is a text file.
   • AIMIRC.INI, which is a text file.
   • BNC.DLL (5,573 bytes), which is a script file.
   • DTKODE.TXT (101,914 bytes), which is a script file.
   • REMOTE.INI, which is a script file.
   • SCRIPT1.DLL (610 bytes), which is a script file.
   • SPIG.TXT (4,340 bytes), which is a script file.
   • SYSBOOT.DLL (453 bytes), which is a script file.
   • TEMP (24,515 bytes), which is a script file.
   • UNICOD_R (877 bytes), which is a script file.
   • WIND.DLL (3,849 bytes), which is a script file.
   • IPSERVER.TXT, which is a text file that contains some URLs.
   • NICKS.TXT, which is a text file that contains mIRC nicknames.
   • UNICOD_L, which is zero bytes when created.
   • BOOT.exe (35,328 bytes), which is a legitimate remote process launcher, Psexesvc.exe. The Trojan attempts to use this utility to copy itself to other systems.
   • EMPAVMS.exe (20,992 bytes), which is a legitimate utility used to hide windows.
   • LIBPARSE.exe (25,600 bytes), which is a process viewer.
   • MOO.DLL (34,304 bytes).
   • NHTML.DLL (6,656 bytes).
   • RESTART.exe (37,888 bytes), which is a utility used to reboot the computer.
   • BLA.TXT (8,397 bytes), which is Backdoor.IRC.Flood.
   • CRAZY.exe (17,408 bytes), which is Hacktool.DoS.
   • CONFIG.HFG (6,209 bytes), which is IRC Trojan.
   • CSCAN.DAT (2,017 bytes), which is IRC Trojan.
   • IMPVMS.DLL (18,355 bytes), which is IRC Trojan.
   • MSCCL.DLL (18,919 bytes), which is IRC Trojan.
   • NVDRV.OCX (18,920 bytes), which is IRC Trojan.
   • REG.XPL (2,707 bytes), which is IRC Trojan.
   • SYSTE32.DLL (1,603 bytes), which is IRC Trojan.
   • MICONFIG.exe (14,336 bytes), which is Hacktool.
   • System.exe (17,920 bytes), which is Hacktool.
   • lan.bat (84,694 bytes), which is BAT.Trojan.
   • Wincmd34.bat (30,993 bytes), which is BAT.Trojan.
   • Expl32.exe (629,760 bytes), which is Backdoor.IRC.Ratsou. This file is a patched version of mIRC.exe.
   • Ratsou.exe (2,351 bytes), which is Trojan.Downloader.Aphe.
     
     
3. Adds the value:
   
   "explorer"="%Windir%help oursexpl32.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   so that this patched mIRC program runs when you restart Windows.
   
   
4. Hooks the IRC file extensions in HKEY_LOCAL_MACHINSoftwareClasses that call %Windir%help oursexpl32.exe when chat files are opened.
   
   
5. Runs %Windir%help oursexpl32.exe in the background.
   
   
6. Uses the dropped impvms.dll file to connect to some randomly generated IP addresses. Then, the Trojan uses the dropped batch files to connect to the remote IPC$ and ADMIN$ shares on each of the IP addresses that it finds, by using various user name and password pairs, and attempts to copy and run the Ratsou.exe file on the remote systems.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
• Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
• Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.

REMOVAL

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Run a full system scan and delete all the files detected as viral. Delete all the files in the %Windir%HelpTours folder.
3. Delete the value that was added to the registry.
   

For specific details on each of these steps, read the following instructions.

1. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).
  
  The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

2. Scanning for and deleting the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan All Files."
2. Run a full system scan.
3. If any files are detected as infected by any of the threats described in the Technical Details section, click Delete.
4. Delete the %Windir%HelpTours folder.

3. Deleting the value from the registry

CAUTION: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

1. Click Start, and then click Run. (The Run dialog box appears.)
2. Type regedit
   
   Then click OK. (The Registry Editor opens.)
   
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete the value:
   
   "explorer"="%Windir%help oursexpl32.exe"
   
   
5. Exit the Registry Editor.