Sanctum Inc. - Vulnerability Alert - Nimda

	Nimda Introduction

	Nimda (ADMIN spelled backwards) is a new powerful worm that is spreading aggressively over the internet. This Trojan worm uses three modes for propagation. It spreads via email, network shares, or through web servers with IIS installed using the IIS Web Directory Traversal exploit. Simply visiting an infected Web page infects Internet users. One aspect of Nimda's versatility is its ability to modify Web sites to carry files that can spread via downloads. Unlike Code Red, the worm can infiltrate a corporate network and create a user account with unlimited access to files and e-mail. Nimda can corrupt servers and email systems, and has forced many companies around the world to shut down systems entirely.

	Result

	Corrupted files and access to sensitive data - the readme.exe file executes a program that opens up the computer�s hard drive for outside access Illegal access to backend systems via the internet - Opens up your internal files to other hackers via the Internet Once it gains control, it scans web servers for other known vulnerabilities and attacks those servers Spreads by emailing itself to everyone in the user�s address book thus overloading the network Forces companies to shutdown networks including all web servers to stop the spread

	Method of Attack

	This worm can be activated in many different ways. Nimda can be triggered through some common actions, such as clicking on an e-mail attachment or running an executable program. The Nimda worm spreads by sending infected e-mails that carry an attachment labeled "readme.exe." It also propagates by infiltrating unsecured Web sites and attaching itself to an unsuspecting computer user's Web browser. "Nimda" may show up as a sound or .wav file. When a user opens the underlying file, called "readme.exe," the program opens the computer's hard drive, allowing the computer to be accessed by third parties via the Internet. The worm can also e-mail itself to everyone in the user's computer-based address book. The worm, like code red, attempts to infect its local sub net first, then spreads beyond the local address space. Nimda has its own e-mail engine and will try to send itself out using addresses stored in e-mail programs. It also scans IIS servers looking for the known vulnerability and attacks those servers. When Nimda strikes a web server, the following will appear in your IIS log file: GET /scripts/root.exe?/c+dir GET /MSADC/root.exe?/c+dir GET /c/winnt/system32/cmd.exe?/c+dir GET /d/winnt/system32/cmd.exe?/c+dir GET /scripts/..%5c../winnt/system32/cmd.exe?/c+dir GET /_vti_bin/..%5c../..%5c../..%5c../winnt/system32/cmd.exe?/c+dir GET /_mem_bin/..%5c../..%5c../..%5c../winnt/system32/cmd.exe?/c+dir GET /msadc/..%5c../..%5c../..%5c/..\xc1\x1c../.. \xc1\x1c../..\xc1\x1c../winnt/system32/cmd.exe?/c+dir GET /scripts/..\xc1\x1c../winnt/system32/cmd.exe?/c+dir GET /scripts/..\xc0/../winnt/system32/cmd.exe?/c+dir GET /scripts/..\xc0\xaf../winnt/system32/cmd.exe?/c+dir GET /scripts/..\xc1\x9c../winnt/system32/cmd.exe?/c+dir GET /scripts/..%35c../winnt/system32/cmd.exe?/c+dir GET /scripts/..%35c../winnt/system32/cmd.exe?/c+dir GET /scripts/..%5c../winnt/system32/cmd.exe?/c+dir GET /scripts/..%2f../winnt/system32/cmd.exe?/c+dir


	Sanctum Stops the Nimda Worm

	AppShield Nimda opens any and all files on your hard drive including internal directories and root files (root.exe) exposing all your mission critical information. This is recognized by AppShield as forceful browsing or a backdoor/debug vulnerability and therefore unauthorized behavior. AppShield will block this behavior from occurring and therefore prevent any manipulation of the business logic on your hard drive as a result of this attack. Similarly, Nimda also tries to execute commands via the web server (Stealth Commanding), and AppShield will stop this malicious behavior as well before your server corrupts others in the line of fire. AppShield automatically blocks all attacks against unpatched IIS systems. AppShield blocks requests for pages that were not requested by a valid authorized web page. Therefore any request for the following pages would be disallowed as none of these are valid pages that would be called directly by another web page. `get_mem_bin vti_bin owssvr.dll Root.exe CMD.EXE ../ (Unicode) Getadmin.dll Default.IDA /Msoffice/ cltreq.asp` Finally, AppShield blocks all requests containing non-safe characters. For instance, all high-bit Unicode characters are by default non-safe. AppScan The worm is injected through the use of known IIS vulnerabilities. AppScan can scan for those vulnerabilities and provide the detailed application risk assessment required to alert users to the severity of their application vulnerability with a link to the patch or coding technique required to avoid further destruction Contacts: Izhar Bar-Gad Sanctum, Inc. Phone: (408) 352-2000 EMail: [email protected] Additional Information: CERT® Advisory CA-2001-26 Nimda Worm Incidents.org—NIMDA Worm/Virus Report — Preliminary

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