Backdoor.IRC.Cirebot

SUMMARY

Backdoor.IRC.Cirebot is a Trojan Horse that exploits the Microsoft DCOM RPC vulnerability (described in Microsoft Security Bulletin MS03-026) by installing a backdoor Trojan Horse on vulnerable systems. Backdoor.IRC.Cirebot consists of a Backdoor component and a Hacktool component, which installs the backdoor on systems that are vulnerable to the exploit.

Some signs of infection may include:

• The existence of the file C:Rpc.exe, C:Rpctest.exe, or C:Lolx.exe. This could indicate that the computer has been infected.
• Traffic on port 445 to sequential IP addresses, which can indicate that the network is being attacked.
• An open port 57005 and an FTP connection on port 69 can indicate that the attack was successful, allowing access to a remote shell and the downloading of the backdoor.

Protection

• Virus Definitions (LiveUpdate™ Weekly) August 6, 2003
• Virus Definitions (Intelligent Updater) August 4, 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: Medium
• Ports: Opens a remote shell on port 57005.
• Target of Infection: IP addresses starting with 4, 12, 24, 64, 65, 68, 128, 165, 208, 211, 213, 217, 218, or 220.

TECHNICAL DETAILS

Backdoor.IRC.Cirebot is a combination of two components: The Hacktool and Backdoor components.

Hacktool component
The Hacktool component of Backdoor.IRC.Cirebot consists of the following files:

Worm.exe (113507 bytes)
Worm.exe is an installer that creates the following files:
• C:Rpc.exe
• C:Rpctest.exe
• C:Tftpd.exe

Rpc.exe (40960 bytes)
Rpc.exe is an "autorooter" tool that does the following:
1. Launches Tftpd, an ftp server. This allows the backdoor to be downloaded from the system that is running the server.
   
   
2. Tries to establish a connection on port 445 to random IP addresses of the form A.B.C.D, in which:
   
   A is one of the following numbers: 4, 12, 24, 64, 65, 68, 128,165, 208, 211, 213, 217,218, 220.
   B is a random number from 0 to 255.
   C and D could be any number (the tool tries every possible value in order).
   
   For instance, if A = 24 and B = 111, it will try to connect to each the following addresses:
   
   24.111.0.1
   24.111.0.2
   24.111.0.3
   ...
   24.111.0.254
   24.111.0.255
   24.111.1.1
   24.111.1.2 . . . and so on.
   
   
3. When a connection is established, it uses Rpctest.exe to open a remote command shell.
   
   
4. Then, it sends commands through the shell to fetch the backdoor using Tftpd and to start the backdoor on the remote system.

Rpctest.exe (94298 bytes)
Rpctest.exe is an exploit tool that takes an address as an argument, applies the RPC buffer overflow exploit, and if successful, returns a command shell request on port 57005.

Tftpd.exe (143842)
Tftpd.exe is a non-malicious FTP server that listens for a connection on port 69.

Backdoor component
The Backdoor component of Backdoor.IRC.Cirebot consists of the file Lolx.exe or Dcomx.exe (26144 bytes). This backdoor Trojan Horse is based on Sdbot.
Like all IRC Trojans, this backdoor component connects to IRC, joins a channel, and waits for commands.

The capabilities of this backdoor component include:

• Using ICQ to send a notification message when the backdoor is started
• Downloading and executing files
• Ending running processes
• Dynamically updating the installed Trojan
• Performing Denial of Service (DoS) attacks
• Stealing CD keys
• "Securing" the machine by removing network shares
• Logging keystrokes
• Attacking other systems using various exploits

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. Disable System Restore (Windows XP).
2. Update the virus definitions.
3. Restart the computer in Safe mode or VGA mode.
4. Run a full system scan and delete all the files detected as Backdoor.IRC.Cirebot.

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

1. Disabling System Restore (Windows XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or the following article, "How to turn off or turn on Windows XP System Restore"

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. 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.

3. Restarting the computer in Safe mode or VGA mode

Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.

• For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
• For Windows NT 4 users, restart the computer in VGA mode.

4. 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 Backdoor.IRC.Cirebot, click Delete.