FreeBSD.Scalper.Worm

SUMMARY

This worm uses the Apache HTTP Server chunk encoding stack overflow vulnerability to spread itself. Currently it has only been confirmed that this worm works on the FreeBSD platform. FreeBSD is an advanced operating system for Intel ia32 compatible, DEC Alpha, and PC-98 architectures. It is derived from BSD UNIX, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals.

This worm has received some media coverage but we believe it is currently not prevalent in the wild. So far, we have not received any customer reports of this worm. For information regarding the vulnerability, please click here.

Protection

• Virus Definitions (LiveUpdate™ Weekly) July 3, 2002
• Virus Definitions (Intelligent Updater) June 28, 2002

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 3 - 9
• Geographical Distribution: Medium
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low
• Payload: Performs TCP, UDP, DNS, and E-mail flooding
• Large Scale E-mailing: Contains the functionality to sent e-mail spam to all e-mail addresses found on the infected machines
• Releases Confidential Info: allows unauthorized access to the infect machine
• Degrades Performance: performs many port 80 requests which could cause internet degradation
• Compromises Security Settings: allows unauthorized access to the infect machine

Distribution

• Distribution Level: Low
• Ports: 2001
• Target of Infection: unpatched Apache Webservers on the FreeBSD operating system

TECHNICAL DETAILS

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":

• 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

Update the virus definitions, run a full system scan, and delete all files that Norton AntiVirus (NAV) detects as FreeBSD.Scalper.Worm. Delete the files, /tmp/.uua or /tmp/.a if they exist.