Virus Alert To Linux Users
Posted 28th Narch 2001

The SANS Institute (through its Global Incident Analysis Center) uncovered a dangerous new worm that appears to be spreading rapidly across the Internet. It scans the Internet looking for Linux computers with a known vulnerability. It infects the vulnerable machines, steals the password file (sending it to a China.com site), installs other hacking tools, and forces the newly infected machine to begin scanning the Internet looking for other victims. Several experts from the security community worked through the night to decompose the worm's code and engineer a utility to help you discover if the Lion worm has affected your organization. Updates to this announcement will be posted at the SANS web site

DESCRIPTION The Lion worm is similar to the Ramen worm. However, this worm is significantly more dangerous and should be taken very seriously. It infects Linux machines running the BIND DNS server. It is known to infect bind version(s) 8.2, 8.2-P1, 8.2.1, 8.2.2-Px, and all 8.2.3-betas. The specific vulnerability used by the worm to exploit machines is the TSIG vulnerability that was reported on January 29, 2001. The Lion worm spreads via an application called "randb". Randb scans random class B networks probing TCP port 53. Once it hits a system, it checks to see if it is vulnerable. If so, Lion exploits the system using an exploit called "name". It then installs the t0rn rootkit.

Once Lion has compromised a system, it:

- - Sends the contents of /etc/passwd, /etc/shadow, as well as some network settings to an address in the china.com domain.

- - Deletes /etc/hosts.deny, eliminating the host-based perimeter protection afforded by tcp wrappers.

- - Installs backdoor root shells on ports 60008/tcp and 33567/tcp (via inetd, see /etc/inetd.conf) - - Installs a trojaned version of ssh that listens on 33568/tcp

- - Kills Syslogd , so the logging on the system can't be trusted

- - Installs a trojaned version of login - - Looks for a hashed password in /etc/ttyhash

- - /usr/sbin/nscd (the optional Name Service Caching daemon) is overwritten with a trojaned version of ssh. The t0rn rootkit replaces several binaries on the system in order to stealth itself. Here are the binaries that it replaces: du, find, ifconfig, in.telnetd, in.fingerd, login, ls, mjy, netstat, ps, pstree, top

- - "Mjy" is a utility for cleaning out log entries, and is placed in /bin and /usr/man/man1/man1/lib/.lib/.

- - in.telnetd is also placed in these directories; its use is not known at this time.

- - A setuid shell is placed in /usr/man/man1/man1/lib/.lib/.x.

DETECTION AND REMOVAL

We have developed a utility called Lionfind that will detect the Lion files on an infected system. Simply download it, uncompress it, and run lionfind. This utility will list which of the suspect files is on the system. At this time, Lionfind is not able to remove the virus from the system. If and when an updated version becomes available (and we expect to provide one), an announcement will be made at this site. Download Lionfind at http://www.sans.org/y2k/lionfind-0.1.tar.gz.