Backdoor.Tuckist

SUMMARY

Backdoor.Tuckist is a Trojan horse program that runs on Linux systems running kernel 2.2.x or 2.4.x. It opens a back door on the compromised computer and is able to hide its files, processes and open ports.

Note: Virus definitions dated November 17th, 2005 or earlier may detect this threat as Backdoor.Suckit.

Protection

• Virus Definitions (LiveUpdate™ Weekly) November 16, 2005
• Virus Definitions (Intelligent Updater) November 16, 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: Medium
• Payload: Allows unauthorized access.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Backdoor.Tuckist is executed, it performs the following actions:

1. Creates the following file:
   
   [RANDOM FILE NAME].elf (29476 bytes)
   
   
2. May create the following file:
   
   /sbin/initsk[RANDOM NUMBERS]
   
   so that the threat runs every time the computer starts.
   
   
3. Attempts to open a shell on the compromised computer.
   
   
4. Attempts to open raw sockets and can be configured to open and listen on ports used by other legitimate applications.
   
   
5. Opens a remote shell that allows the attacker to control the compromised computer when the attacker sends a specially crafted TCP packet to a configured port (usually port 80).
   
   
6. Attempts to hide its presence on the compromised computer by hiding the process.
   
   
7. Allows an attacker to hide any other process, ports, and files.
   
   
8. May install a network packet sniffer that is able to scan the network traffic, gathering user names and passwords for many Linux services, such as telnet, ssh, scp, rsh, and mysql.
   
   
9. Attempts to hook and modify the following system objects by writing directly into the /dev/kmem file, which controls kernel memory:
   
   
   • IDT
   • sys_call

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

If your Symantec antivirus product detects Backdoor.Tuckist, delete the infected files.

Once the threat attacks a computer, it is difficult to determine what else the computer has been exposed to. In most cases, changes other than those made by the threat will not have occurred. However, the author of the threat may have been able to use the threat to access the computer to make changes to it. Unless you can be absolutely sure that malicious activity has not been performed on the computer, we recommend completely reinstalling the operating system.