__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Center ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Cisco Secure IDS Signature Obfuscation Vulnerability October 1, 2001 17:00 GMT Number M-001 ______________________________________________________________________________ PROBLEM: Two Cisco Intrusion Detection Systems have a vulnerability that allows the %u encoding technique to circumvent them. PLATFORM: * Cisco Secure Intrusion Detection System, formerly known as NetRanger, Sensor component * Cisco Catalyst 6000 Intrusion Detection System Module DAMAGE: The vulnerability may allow attacks to go undetected and thus unrecorded. SOLUTION: Apply the given patch and/or workaround. ______________________________________________________________________________ VULNERABILITY The risk is MEDIUM. Circumvented Intrusion Detection Systems ASSESSMENT: can impair virus infection investigations. ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/m-001.shtml ORIGINAL BULLETIN: http://www.cisco.com/warp/public/707 /cisco-intrusion-detection-obfuscation-vuln-pub.shtml ______________________________________________________________________________ [****** Start Cisco Security Advisory ******] Summary Intrusion Detection Systems inspect network traffic for suspect or malicious packet formats, data payloads and traffic patterns. Intrusion detection systems typically implement obfuscation defense - ensuring that suspect packets cannot easily be disguised with UTF and/or hex encoding and bypass the Intrusion Detection systems. Recently, the CodeRed worm has targeted an unpatched vulnerability with many MicroSoft IIS systems and also highlighted a different encoding technique supported by MicroSoft IIS systems. This encoding technique known as %u can be used to circumvent intrusion detection systems, and has been made public by eEye security in their announcement located at http://www.eeye.com/html/Research/Advisories/AD20010705.html. Cisco has corrected this vulnerability in the Cisco Secure Intrusion Detection System, formerly known as Netranger, with a service pack that is now available to customers. This vulnerability also affects the Cisco Catalyst 6000 Intrusion Detection System Module, and will be repaired in a service pack for version 3.0, which is not yet released. Cisco has provided a workaround for this issue, which is listed in the Workaround section of this advisory. The complete notice will be available at http://www.cisco.com/warp/public/707 /cisco-intrusion-detection-obfuscation-vuln-pub.shtml. Affected Products The following products are affected: * Cisco Secure Intrusion Detection System, formerly known as NetRanger, Sensor component * Cisco Catalyst 6000 Intrusion Detection System Module Additionally, selected workarounds such as the use of NBAR, or the Cisco Cache Engine, for filtering the CodeRed worm exploit will not detect %u encoding attack obfuscation, unless specifically configured for all possibilities. The Cisco Secure Intrusion Detection System Director for both Unix and NT platforms are management components of the IDS, and do not participate in packet obfuscation detection, and are not affected by this vulnerability. The following products implement a limited subset of Intrusion Detection attack signatures, and the signatures included do NOT detect MicroSoft IIS targeted attacks, and are therefore NOT vulnerable to the %u encoding method of attack obfuscation. * Cisco Secure PIX Firewall * Cisco IOS Firewall Feature Set with Intrusion Detection Details The "CodeRed" worm utilized an obscure unicode encoding technique to deliver the payload of the worm. The %u encoding method is a different encoding method that is understood and parsed by the IIS web server. This encoding can be applied to other portions of the url to effectively obfuscate the attack, preventing detection by many intrusion detection systems available. Cisco Secure Intrusion Detection System Sensor decoding algorithms have been modified to detect and parse this unicode form. Cisco Catalyst 6000 Intrusion Detection Systems Modules do NOT yet implement obfuscation detection. This vulnerability is documented as Cisco Bug ID CSCdv20287. This vulnerability is also listed in the Mitre CVE as CAN-2001-0669. Impact This method of obfuscation can allow malicious exploitation to bypass current intrusion detection technology. Software Versions and Fixes This vulnerability is repaired in service pack 3.0(2)S6 for the Cisco Secure Intrusion Detection System Sensor, and will be included in all versions forward. This service pack is still officially BETA code until the testing cycle is complete; however, due to the nature of the repairs and the public notification of this vulnerability, the code is posted for customer download at the following location: ftp://ftp-eng.cisco.com/csids-sig-updates/ServicePacks /IDSk9-sp-3.0-1.43-S6-0.43-.bin This vulnerability will be repaired in service pack 3.0 for the Cisco Catalyst 6000 Intrusion Detection Module. Basic obfuscation detection was originally slated for the 3.0 release, which is due to be available in early October 2001. A service pack to the 3.0 release will include this additional method of obfuscation, but will not be available until after the October 2001 release. Cisco will update this advisory when more detailed delivery information for the service pack is available. Obtaining Fixed Software Cisco is offering software upgrades to remedy this vulnerability for all affected customers who have current SmartNet contracts on their sensors. Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained via the Software Center on Cisco's Worldwide Web site at http://www.cisco.com. Customers without contracts can purchase either SmartNet contracts or one time software upgrades (IDS-SW-U) for each affected sensor by contacting the Customer Service Center. Customer Service contacts are as follows: +1 800 553 6378 (toll-free from within North America) +1 408 526 1868 (toll call from anywhere in the world) See http://www.cisco.com/public/ordering_info.shtml for more information on ordering Cisco products and upgrades. Customers can also contact the Cisco Technical Assistance Center (TAC). TAC contacts are as follows: * +1 800 553 2447 (toll-free from within North America). * +1 408 526 7209 (toll call from anywhere in the world). * E-mail: tac@cisco.com See http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including instructions and e-mail addresses for use in various languages. Please do not contact either "psirt@cisco.com" or "security-alert@cisco.com" for software upgrades. Workarounds Workarounds for this issue exist for both the Cisco Secure Intrusion Detection System Sensor, and the Catalyst 6000 Intrusion Detection System Module. A custom string match signature can be defined to address the %u unicode obfuscation vulnerability. This custom string match will detect uses of the unicode obfuscation. There may be legitimate uses of the unicode strings that are non-threatening that we are unaware of, so this signature may alarm on legitimate traffic patterns. Careful monitoring of associated alarms must accompany this signature. Signature 1 ****************************************** Unicode Obfuscation String: "[%][uU][0-9a-FA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]" Occurrences: 1 Port: 80 If you have Web servers listening on other TCP ports (for example, 8080), you will need to create a separate custom string match for each port number. Recommended Alarm Severity Level: High (CSPM) 5 (Unix Director) Direction: TO *************************************************************** For more information on Custom String Match features, please refer to the documentation available at http://www.cisco.com/univercd/cc/td/doc/product/iaabu/csids/csids5/csidscog/. Exploitation and Public Announcements This vulnerability has been announced by the eEye security team, and is published on the eEye security site at the following location http://www.eeye.com/html/Research/Advisories/AD20010705.html. Cisco has no knowledge of exploitation of this method of obfuscation. Status of This Notice: INTERIM This is an interim notice. Although Cisco cannot guarantee the accuracy of all statements in this notice, all of the facts have been checked to the best of our ability. Cisco will issue updated versions of this notice when there is updated information on product release dates. Should there be a significant change in the facts, Cisco may update this notice. This notice will be updated by 2001-OCT-15. Distribution This notice will be posted on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707 /cisco-intrusion-detection-obfuscation-vuln-pub.shtml. In addition to Worldwide Web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients: * cust-security-announce@cisco.com * bugtraq@securityfocus.com * firewalls@lists.gnac.com * first-teams@first.org (includes CERT/CC) * cisco@spot.colorado.edu * cisco-nsp@puck.nether.net * comp.dcom.sys.cisco * Various internal Cisco mailing lists Future updates of this notice, if any, will be placed on Cisco's Worldwide Web server, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the URL given above for any updates. Revision History ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Revision 1.0 2001-SEP-05 17:00 US/Pacific Initial public release. ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Revision 1.1 2001-SEP-14 Updated details of workarounds and instructions obtaining fixed software. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Revision 1.2 2001-SEP-27 Updated details of instructions for obtaining fixed software. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Cisco Security Procedures Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707/sec_incident_response.shtml. This includes instructions for press inquiries regarding Cisco security notices. This notice is copyright 2001 by Cisco Systems, Inc. This notice may be redistributed freely after the release date given at the top of the text, provided that redistributed copies are complete and unmodified, including all date and version information. [****** End Cisco Security Advisory ******] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Cisco Systems, Inc. for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Center, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 (7x24) FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@ciac.org Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ Anonymous FTP: ftp.ciac.org PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) L-135: SGI File Globbing Vulnerability in ftpd L-136: HP-UX Security Vulnerability in PRM L-137: FreeBSD lpd Remote Root Vulnerability L-138: Gauntlet Firewall CSMAP and smap/smapd Buffer Overflow Vulnerability L-139: Microsoft IIS "%u encoding IDS bypass vulnerability" L-140: Gauntlet Firewall CSMAP and smap/smapd Buffer Overflow Vulnerability L-141: RSA BSAFE SSL-J 3.x Vulnerability L-142: RPC Endpoint Mapper Vulnerability L-143: HP libsecurity Vulnerability L-144: The W32.nimda Worm