-----BEGIN PGP SIGNED MESSAGE----- Cisco Security Advisory: Cisco Secure Intrusion Detection System Signature Obfuscation Vulnerability ======================================================================= Revision 1.0 For release 2001 September 5 05:00 PM US/Pacific (UTC -0700) ------------------------------------------------------------------------ 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. 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-3.0-1.42-S6 - -0.42-.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. Getting Fixed Software ====================== Cisco is offering free software upgrades to remedy this vulnerability for all affected customers. 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 should get their upgrades by contacting 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: tacat_private 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. Give the URL of this notice as evidence of your entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC. Please do not contact either "psirtat_private" or "security-alertat_private" for software upgrades. Workarounds =========== Workarounds for this issue would include implementing a large number of custom string match entries, each one an iteration of the proprietary encoding obfuscation method for the expected attack. This workaround could possibly address a short term problem, but is not scalable for the majority of customers, and the product upgrade or service pack is recommended. 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-announceat_private * bugtraqat_private * firewallsat_private * first-teamsat_private (includes CERT/CC) * ciscoat_private * cisco-nspat_private * 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 For public release 2001-SEP-05 17:00 US/Pacific (UTC-0700) 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. ------------------------------------------------------------------------ -----BEGIN PGP SIGNATURE----- Version: PGP 7.0 iQEVAwUBO5cL5Q/VLJ+budTTAQHh0Qf+ImavBMmj0HQLKX67tL0jP8HYvt7awb2P aArj23gVw9QFFAM/UaLE1euNtdUZsLhWCDyZ4vLISPYap7lwozFz+11PTo/IIuKS Ruk1VlS/6+LknDpqgydEmoyZwuSYkm+c9sQwjccO7GusNMY5WWg4iFgsmKCTfct1 NhfrUUPr0GsuOqbnrNy83sD+0sC2LlwRmWEG1F5EZKJwmUvWSRwu/EG/KW9H8JBh hGVcsM+R87d88dDr2muje+F2cv7s1/0rV7dOPIKOhV+JuDWz3FsT//w/i0peJzhN C5U1W/hxO5KbgKcPKAeA9LFyF6kxv8A7LNYhwwM1EQ5pLwFOeGpkeA== =9IOH -----END PGP SIGNATURE-----
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