Linux.Adore.Worm

When the worm is executed it attempts to download a tar file from the following location:
go.163.com

This site appears to have been closed, causing the worm to no longer be effective.

If the worm is able to download the file from the above location, it performs the following actions:

• The worm untars the file to /usr/lib/lib and executes a script, which begins the worm routine.
• It replaces ps with a Trojanized version, and backs up the original to /usr/bin/adore.
• Next, the worm adds a script to the daily cron job, which kills all of its processes except the installed backdoor by rebooting or using killall on the appropriate processes. The script also replaces the Trojanized ps. This allows the worm to propagate for a limited amount of time, but reduces the chances of being detected.
• Linux.Adore.Worm then adds the users ftp and anonymous to /etc/ftpusers, blocking the wuftpd hole, which is exploited. The worm also kills the rpc.statd, rpc.rstatd, and lpd processes, preventing those vulnerabilities from being exploited.
• Next, the worm replaces klogd (kernel message logger) with a backdoor program that uses ICMP instead of the traditional TCP or UDP methods. The backdoor allows root shell access.
• The worm then sends information to two of four email addresses located in China. The ISP has been notified accordingly. The information includes the IP address of the compromised computer, the process list, the history, hosts file, and shadow password file.
• Finally, the worm executes the routines to find new systems to compromise. The worm generates random class-B IP addresses and checks to see if they are vulnerable to the common statd, lprng, wuftp, and bind vulnerabilities. If vulnerable, the worm exploits the vulnerability to gain access to the system.

Information on patching the four vulnerabilities including links to patches can be found at:

• LPRng: http://www.cert.org/advisories/CA-2000-22.html
• wu-ftpd 2.6: http://www.cert.org/advisories/CA-2000-13.html
• Bind: http://www.cert.org/advisories/CA-2001-02.html
• rpc.statd: http://www.cert.org/advisories/CA-2000-17.html

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
• 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.
• Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
• Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
• Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
• Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
• If a 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate compromised computers quickly to prevent threats from spreading further. 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.
• If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
• For further information on the terms used in this document, please refer to the Security Response glossary.

Summary