Backdoor.Dextenea

SUMMARY

Backdoor.Dextenea is a Linux-based Trojan horse that attempts to open a back door and uses various malicious programs to conceal its presence.

Protection

• Virus Definitions (LiveUpdate™ Weekly) March 25, 2005
• Virus Definitions (Intelligent Updater) March 24, 2005

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
• Payload: Opens a back door

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Backdoor.Dextenea runs, it does the following:

1. Creates the following files:
   
   
   • /usr/secure (2712 bytes)
   • /usr/doc/sys/qrt (96778 bytes)
   • /usr/doc/sys/run (6086 bytes)
   • /usr/doc/sys/crond (9259 bytes)
   • /usr/sbin/kfd (8776 bytes)
     
     
2. Replaces the following legitimate files with copies of the Trojan to hide its presence:
   
   
   • /bin/ps or /usr/bin/ps (16419 bytes)
   • /bin/netstat or /usr/bin/netstat (variable size)
     
     
3. Creates the following directories:
   
   
   • /lib/security/.config/ssh
   • /usr/doc/kern
   • /usr/doc/backup
   • /usr/doc/backup/txt
   • /lib/backup
   • /lib/backup/txt
   • /usr/doc/work
   • /usr/doc/sys
     
     
4. Attempts to copy a script file named S80rpcmap into the following directories, so that the Trojan starts when Linux starts:
   
   
   • /etc/rc.d/rc2.d
   • /etc/rc.d/rc3.d
   • /etc/rc.d/rc4.d
   • /etc/rc.d/rc5.d
     
     
5. Installs a telnet and a modified SSH Deamon as back doors. The attacker will be able to connect to the infected computer using a password and IP port of his or her choosing.
   
   
6. Creates a user named r00t, so that the attacker can connect to the compromised computer using SSH.
   
   
7. Attempts to install several of the following root kits, hack tools, and network scanners, which allows the attacker to use the compromised computer to attack other computers:
   
   
   • kfence
   • adore
   • psybnc
   • flood
   • mole
   • selena
     
     
8. Sends an email containing information about the compromised computer to a predetermined email address.

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.Dextenea.

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

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 daily. 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 latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions. For detailed instructions read the document: How to update virus definition files using the Intelligent Updater.

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.Dextenea, click Delete.