FreeBSD.Scalper.Worm

The worm will attempt to locate vulnerable computers on a set of IP class ranges that is hard-coded in the worm. An example of an IP class range would be 55.xxx.xxx.xxx. The only hard coded value is the first element in the IP, the second element is randomly generated, and the third and fourth elements are scanned incrementally.

It sends a port 80 HTTP GET request to all IP addresses and when it finds an Apache server, it attempts to use the Apache HTTP Server chunk encoding overflow vulnerability to execute a remote shell command and simulate a handshake between the infected computer and the vulnerable computer.

The worm sends itself in UUEncoded form to the remote computer as the file /tmp/.uua. It then decodes and executes /tmp/.a after setting /tmp/.a to executable. The worm also kills all previously installed copies of the worm on the vulnerable computer.

Upon execution the worm open UDP port 2001 to listen for remote instructions. These remote instructions will perform one of the following functions:

• Collect email addresses from the infected computer
• View Web pages
• Send email messages (spam)
• TCP, UDP, DNS Flooding
• Execution of shell commands
• Other Denial of Service functions.

NOTE: Currently Symantec Security Response has identified 2 variants of this worm.

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