Trojan.Slanret

SUMMARY

Trojan.Slanret is a Trojan horse that allows a hacker to gain full access to your computer.

If a program was set up to use this Trojan, the Trojan makes the program completely stealth when the program runs. The Trojan hides the file, process, and registry keys of the program. So, it is not possible to see the program using Windows Explorer or any other normal, user-level application.

Any registry keys that the program created will not be visible using applications such as the Windows Registry Editor.

Backdoor.Krei is one backdoor Trojan known to use Trojan.Slanret to hide its malicious activities.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) February 5, 2003
• Virus Definitions (Intelligent Updater) January 30, 2003

Threat Assessment

Wild

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

Damage

• Damage Level: Low

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Trojan.Slanret is a driver that uses the file name ierk8243.sys. Once the threat is installed on the system, it creates an interface that different programs can use.

If a program is set up to use this Trojan, the program gains full system privileges. Also, the program becomes completely stealth, which means that any normal, user-level application will not be able to view the file of the program. Any registry keys or processes that the program created will not be visible either.

Once Trojan.Slanret is removed from the system, any program (as well as the registry keys or processes created) that used it will be visible again.

When the Trojan is installed on the system, it creates a device named Mp437bba8e. The Trojan hooks several service functions in Windows. Then, the programs can use the device that this Trojan installed to perform malicious actions on the system.

Even though Trojan.Slanret is stealth, on Windows 2000/XP computers it is possible to see whether it runs on a system as a driver. To do this:

1. Click Start, point to Programs, point to Accessories, point to System Tools, and then click System Information. The Microsoft System Information window appears.
2. In the left pane, double-click Software Environment, and then click Drivers.
3. In the right pane, look for ierk8243.sys. If this driver is displayed, it indicates that Trojan.Slanret is running on the system.

Unconfirmed reports indicate that the following registry key is added to the system to load Trojan.Slanret when you start Windows:

HKEY_LOCAL_MACHINESystemCurrentControlSetServicesIerk8243

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

As it is not possible to guarantee the integrity of the infected system, we strongly recommend that you follow the procedure described in the Additional information section.

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 Trojan.Slanret.
3. Delete the registry key:
   
   HKEY_LOCAL_MACHINESystemCurrentControlSetServicesIerk8243
   

For specific details on each of these procedures, 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 the 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), in the "Protection" section, at the top of this writeup.
• 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), in the "Protection" section, at the top of this writeup.
  
  The Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

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 with Trojan.Slanret, click Delete.

3. Deleting the value from the registry

CAUTION: Symantec strongly recommends that you back up the registry before you make 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, and then click OK. (The Registry Editor opens.)
3. Navigate to and delete the key:
   
   HKEY_LOCAL_MACHINESystemCurrentControlSetServicesIerk8243
   
   CAUTION: Make sure that you delete only the Ierk8243 subkey. Do not delete the Services parent key.
   
4. Exit the Registry Editor.