Linux.Ramen.Worm

Linux.Ramen is a worm that is in the wild. It spreads over the Internet onto machines running Red Hat 6.2 or Red Hat 7.0. Since this worm only operates on the Linux operating system, users of Microsoft Windows will be largely unaffected.

The worm starts by running a shell script called start.sh. This script calls a random number generator that returns a random class B subnet IP address. The worm will attempt to copy itself to these IP addresses. The worm then starts an HTTP server on port 27374 to serve out itself to newly infected machines and also patches the exploits that it used to gain access to the system.

By plugging these holes, the worm will not reinfect the machine. In addition, as an indirect effect, other hackers will not be able to gain access to these machines using these exploits.

The worm uses a tool called synscan which has been modified to fit its needs. Using this tool, the worm contacts a randomly generated IP address and checks the FTP banner to determine if the machine is running Red Hat Linux 6.2 or Red Hat Linux 7.0. For machines running Red Hat 6.2, the worm will attempt to exploit a vulnerable rpc.statd or wuftpd service. For Red Hat 7.0, the worm tries to exploit an LPRng bug to gain access to the system.

Once the worm gains access to the system using the above exploits, the worm copies itself as a tar.gz package onto the newly compromised system. The worm does so by downloading the tar.gz package from the infecting machine by means of the worm-created HTTP service running on port 27374.

The worm extracts the contents of this package into the tmp directory on the attacked machine and executes start.sh, activating the worm on the newly infected machine.

An email message is also sent to an anonymous Yahoo! and Hotmail email account specifying the IP address of the attacked machine. Most likely, these email accounts belong to the author of this worm allowing the author to keep track of machines that are infected.

Finally, the worm replaces Index.html to show the following contents:

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