Internet Security Systems Security Alert January 18, 2000
Ramen Linux Worm Propagation
A self-propagating worm known as Ramen is currently exploiting well-known holes in unpatched Red Hat Linux 6.2 systems and in early versions of Red Hat 7.0. In addition to scanning for additional systems and propagating to vulnerable systems, the worm also defaces Web servers it encounters by replacing the "index.html" file. It may also interfere with some networks supporting multicasting.
Ramen is currently known to attack Red Hat systems running vulnerable versions of wu-ftp, rpc.statd, and LPRng. New exploits can be added to the existing worm to expand its capabilities.
Ramen combines several known exploits and tools using a set of scripts. The initial attack starts with a scan for port 21 (FTP) and the retrieval of any FTP banners for any FTP services it encounters. The script uses this information to determine if it has contacted a system that may be vulnerable to one of its packaged exploits. Currently, Ramen uses the date encountered in the FTP banner of the system being scanned.
If a vulnerable system is detected, the worm starts a propagation script based on what vulnerability is likely to be present. The propagation scripts and exploits run in parallel with the scanning process.
Using one of the exploitable services, Ramen executes a command on the target system that creates a working directory for itself, "/usr/src/.poop". Ramen then requests a copy of itself, ramen.tgz, from the attacking system using Linux web browser and the Web-like service it installs on compromised systems.
When installed on the new system, Ramen attempts to set up very limited Web-like service on port 27374 to provide for further distribution of the Ramen package. The service uses port 27374 to provide a copy of the ramen.tgz package to any connection with any request on that port.
Ramen searches the entire system, including any remotely mounted file systems, and replaces any file named "index.html" with a copy of its own page. This not only defaces any web site that it encounters, but also corrupts html based documentation files and possible working files in personal directories.
E-mail messages are sent to two accounts, email@example.com and firstname.lastname@example.org, from compromised systems. Owners of the systems where the two addresses were hosted have been notified.
Ramen disables existing FTP services (in inetd on Red Hat 6.2 or in xinetd on Red Hat 7.0) and disables rpc.statd. This action may be to prevent any attempts to re-infect the systems with additional copies of the worm.
Ramen continues to propagate by using the newly compromised system to scan Class B (/16) wide address spaces, searching for port 21 (FTP) and looking for new vulnerable hosts.
On networks and ISPs supporting multicasting, the SYN scanning performed by Ramen can disrupt network traffic when scanning the multicast network range.
Ramen is driven by scripts that can be easily modified to attack other versions of Linux or other Unix systems. The exploits included with Ramen are known to work against other versions of these systems, even though Ramen itself is not keyed to trigger on them.
Red Hat 6.2 for Intel not patched for wu-ftp or nfs. Red Hat 7.0 First Edition for Intel not patched for LPRng.
Systems not known to be vulnerable:
Red Hat 7.0 for Intel Second Edition (Respin). Previous versions of Red Hat Linux. Non-Intel versions of Linux. Non-Red Hat versions of Linux. Any other versions of Unix.
Ramen does not attempt to hide its presence or clean up after itself. It can be detected on a system by the presence of the directory /usr/src/.poop or by the presence of the file /sbin/asp.
To remove the Ramen Worm from your system, follow these steps:
Due to the general-purpose exploits at the core of this worm, it is advisable to implement the following safeguards to prevent successful attacks from potential variations of this exploit.
Disable FTP if it is not a required service. FTP provides information that can be exploited to identify vulnerable systems, even when FTP is not vulnerable.
Do not permit outside network access to RPC services, including NFS.
Do not permit outside network access to LPR services.
Install and maintain all security fixes in a timely manner.
Support to detect both the rpc.statd and the wu-ftp vulnerabilities is available to ISS Internet Scanner customers in X-Press Update 4.4. ISS RealSecure support to detect both the rpc.statd vulnerability and the wu-ftp vulnerability is available in X-Press Update SR 1.1. ISS X-Force plans to make support available for the LPrng vulnerability for both Internet Scanner and RealSecure in an upcoming X-Press Update release.
ISS RealSecure customers can configure a Connection Event on port 27374 to detect activity associated with the propagation of this worm and may use the following User Defined signature to detect outbound emails originating from machines infected with the Ramen Worm:
The material contained in this advisory was researched by Michael Warfiled of ISS X-Force.
For additional information refer to the INCIDENTS and VULN-DEV mailing lists hosted at SecurityFocus.com as well as mailing lists hosted on RedHat.com.
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