Backdoor.Dewin

SUMMARY

Backdoor.Dewin allows a hacker to gain access to and remotely control an infected computer. The Trojan program is written in Microsoft Visual C++ and is compressed with PECompact.

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Note: Virus definitions dated prior to June 14, 2002, may detect this threat as Backdoor.Trojan

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Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) June 19, 2002
• Virus Definitions (Intelligent Updater) June 14, 2002

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 50 - 999
• Number of Sites: More than 10
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Medium
• Releases Confidential Info: Password files can be sent to the hacker.
• Compromises Security Settings: Allows unauthorized access to the compromised computer.

Distribution

• Distribution Level: Low
• Ports: 15553/tcp

TECHNICAL DETAILS

When Backdoor.Dewin runs, it does the following:

1. Copies itself as C:\%Windows%Winreg.exe.
   
   

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   Note: %Windows% is a variable. By default, this is C:Windows or C:Winnt. The Trojan locates the Windows folder and copies itself to that location. Some variants of this Trojan create the file, %Windows%svchost.exe.
   

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2. Adds the value:
   
   SystemReg      C:\%Windows%winreg.exe run
   
   
   Some variants add the value:
   
   SystemReg      C:\%Windows%svchost.exe run
   
   to the following registry keys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersion
   RunServices
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun
   HKEY_USERS.DEFAULTSoftwareMicrosoftWindowsCurrentVersionRun
   
   These changes cause the Trojan to be automatically executed when you start Windows.
   
   
3. The Trojan uses TCP port 15553 to connect to the remote attacker.
   
   
4. The Trojan may create the following files, which it uses to store stolen information:

• C:\%Windows%TempTemp.bat
• C:\%Windows%TempTemp.pif
• C:\%Windows%Asfwin.sys

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Note: These three files are not viral by themselves, therefore, Norton AntiVirus does not detect them. Manually delete them if your computer was infected with Backdoor.Dewin.

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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 Backdoor.Dewin.
3. Delete the values that were added to the registry.

1. To update 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. To scan for and delete 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 with Backdoor.Dewin, click Delete.

3. To remove the value from the registry

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WARNING: 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.

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1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate, in turn, to each of the following keys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersion
   RunServices
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun
   HKEY_USERS.DEFAULTSoftwareMicrosoftWindowsCurrentVersionRun
   
   
4. For each key, delete the following values found from the right pane:
   
   SystemReg      C:\%Windows%winreg.exe run
   
   or:
   
   SystemReg C:\%Windows%svchost.exe run
   
   
5. Click Registry, and then click Exit.