__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Center ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Multiple DoS Vulnerabilities in Cisco Broadband Operating System (CBOS) [Cisco Security Advisory Rev. 1.5] August 9, 2001 23:00 GMT Number L-130 ______________________________________________________________________________ PROBLEM: A specific URL, a stream of TCP SYN packets, and a large ICMP ECHO (PING) can each lock up a router. Intrusion attempts through the router's Web interface are not logged. PLATFORM: Certain combinations of Cisco 600 series routers and CBOS Software as described below. DAMAGE: The vulnerabilities can lead to a Denial-of-Service, and repeated intrusion attempts can go unnoticed. SOLUTION: Upgrade to releases that are not vulnerable as described in Cisco's advisory. ______________________________________________________________________________ VULNERABILITY The risk is MEDIUM. The vulnerabilities and exploits for the ASSESSMENT: Denial-of-Service attacks and unobserved attempted intrusions have been discussed in public forums. ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/l-130.shtml ______________________________________________________________________________ [***** Start Cisco Security Advisory Rev. 1.5 *****] Cisco - Security Advisory: Multiple Vulnerabilities in CBOS Security Advisory: Multiple Vulnerabilities in CBOS Revision 1.5 For Public Release 2000 December 04 08:00 (GMT +0800) Last Update 2001 August 7 Summary Multiple vulnerabilities have been identified and fixed in CBOS, an operating system for the Cisco 600 family of routers. *)Any router in the Cisco 600 family that is configured to allow Web access can be locked by sending a specific URL. Web access is disabled by default, and it is usually enabled in order to facilitate remote configuration. This defect is documented as Cisco bug ID CSCdr98772. *)By sending a stream of TCP SYN packets to the router, it is possible to exhaust all available TCP sockets. The consequence is that no new TCP sessions addressed to the router will be established. The difference between this vulnerability and a SYN Denial-of-Service attack is that this one can be accomplished by a slow stream of packets (one per second). This defect is documented as Cisco bug ID CSCds59206. *)Invalid login attempts using the Web interface are not logged. This defect is documented as Cisco bug ID CSCds19142. *)It is possible to lock up the router by sending a large ICMP ECHO (PING) packet to it. This defect is documented as Cisco bug ID CSCds23921. The following releases of CBOS are vulnerable to all defects: 2.0.1, 2.1.0, 2.1.0a, 2.2.0, 2.2.1, 2.2.1a, 2.3, 2.3.2, 2.3.5, 2.3.7 and 2.3.8. These defects will be fixed in the following CBOS releases: 2.3.5.015, 2.3.7.002, 2.3.9 and 2.4.1. Customers are urged to upgrade to releases that are not vulnerable to this defect as shown in detail in the section Software Versions and Fixes below. This advisory is available at the http://www.cisco.com/warp/public/707/CBOS-multiple.shtml. Affected Products The affected models are: 627, 633, 673, 675, 675E, 677, 677i and 678. These models are vulnerable if they run any of the following, or earlier, CBOS releases: 2.0.1, 2.1.0, 2.1.0a, 2.2.0, 2.2.1, 2.2.1a, 2.3, 2.3.2, 2.3.5, 2.3.7 and 2.3.8. No other releases of CBOS software are affected by this vulnerability. No other Cisco products are affected by this vulnerability. These defects will be fixed in the following CBOS releases: 2.3.5.015, 2.3.7.002, 2.3.9 and 2.4.1. Details CSCdr98772 The behavior is caused by inadequate URL parsing in CBOS. Each URL was expected to terminate with a minimum of a single space character (ASCII code 32, decimal). Sending a URL that does not terminate with a space causes CBOS to enter an infinite loop. It is necessary to power cycle the router to resume operation. To exploit this vulnerability, a router must be configured to accept Web connections. Having a Web access password configured does not provide protection against this vulnerability. CSCds59206 By sending a stream of SYN packets addressed to the router, it is possible to exhaust all available TCP sockets within CBOS. This is due to the memory leak in CBOS. When a router is set into a state where it cannot accept a new connection, it can be maintained in this state by a slow stream of SYN packets until the router is rebooted. The stream can be as slow as one packet per second, so one machine with a 64 KB connection can hold up approximately 150 routers. Note: This does not effect non-TCP traffic. All User Datagram Protocol (UDP) and Internet Control Message Protocol (ICMP) packets can be handled by a router without any problems. All existing and new TCP sessions through the router will not be affected. When an attacking stream is terminated, a router recovers itself within a few minutes. CSCds19142 Using the Cisco Web Management interface, it is possible to keep guessing an access password without those password attempts being logged. A password may be either "exec-only" or "enable". A user with an "exec-only" password cannot change a router configuration. CSCds23921 By sending a large (at least 65500 bytes in size) ICMP ECHO (PING) packet to the router itself, it is possible to overflow an internal variable and cause router lockup. The router is not affected by the packets which are routed through it. Impact CSCdr98772 By sending a tailored URL to a router, it is possible to cause a Denial-of-Service. Every affected router must be powered off and back on in order to restore its normal functionality. CSCds59206 It is possible to prevent all TCP access to a router. This blocks all attempts at remote router administration. CSCds19142 Long term, brute force password guessing can be performed without being noticed. When the correct password is guessed, it can be used to view or modify router configuration. This may be particularly dangerous in installations where multiple routers have the same password. CSCds23921 It is possible to lock up the router thus causing Denial-of-Service. Every affected device must be powered off and back on in order to restore its normal functionality. Software Versions and Fixes The following table summarizes the CBOS software releases affected by the defects described in this notice and scheduled dates on which the earliest corresponding fixed releases will be available. Dates are tentative and subject to change. +---------------+-------------------------+-------------------------------------+ | Major Release | Description or Platform | Availability of Repaired Releases* | +---------------+-------------------------+-----------------+-------------------+ | | Patch release** | General | | | | Availability (GA) | +---------------+-------------------------+-----------------+-------------------+ | All releases | 627, 633, 673, 675, | 2.3.5.015 | - | | | 677, 678 | 2000-DEC-15 | | +---------------+-------------------------+-----------------+-------------------+ | 2.3.7.001 | 677i | 2.3.7.002 | | | | | 2000-DEC-15 | | +---------------+-------------------------+-----------------+-------------------+ | All releases | All platforms | - | 2.3.9 | | | | | 2001-MARCH 19 | +---------------+-------------------------+-----------------+-------------------+ | All releases | All platforms | - | 2.4.1 | | | | | 2000-DEC-15 | +---------------+-------------------------+-----------------+-------------------+ | Notes | +-------------------------------------------------------------------------------+ | * All dates are estimated and subject to change. | | | | ** Patch releases are subjected to less rigorous testing than regular GA | | releases, and may have serious bugs. | +-------------------------------------------------------------------------------+ Obtaining Fixed Software Cisco is offering free software upgrades to eliminate 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 through the Software Center on Cisco's Worldwide Web site at http://www.cisco.com. Customers whose Cisco products are provided or maintained through prior or existing agreement with third-party support organizations such as Cisco Partners, authorized resellers, or service providers should contact that support organization for assistance with the upgrade, which should be free of charge. 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: tac@cisco.com 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 "psirt@cisco.com" or "security-alert@cisco.com" for software upgrades. Workarounds CSCdr98772 There are two workarounds for this vulnerability. The potential for exploitation can be lessened by ensuring that Web access to the router is limited to a legitimate IP address. This can be done by entering the following commands while in enable mode: cbos# set web remote 10.0.0.1 cbos# set web enabled where 10.0.0.1 is the address of the host with a legitimate need for Web access to the router. Alternatively, disabling the Web access completely will also prevent this vulnerability from being exploited. This can be done by entering the following command while in enable mode: cbos# set web disabled Another option is to change the Web port from the default port 80 to some arbitrary port. This will also help in cases where malicious program is making HTTP requests to the default port. This can be accomplished by the following commands: cbos# set web port cbos# write cbos# reboot You must reboot the router in order for changes to take effect. You should also take care to avoid well known ports that are described in RFC1700. CSCds59206 There is no workaround for this vulnerability. CSCds19142 The Web Management interface can be disabled by entering the following commands in enable mode: cbos# set web disabled CSCds23921 All incoming ICMP ECHO (PING) packets destined to the router itself should be denied. That can be achieved by following commands: cbos# set filter number on deny incoming all 0.0.0.0 0.0.0.0 255.255.255.255 protocol ICMP cbos# set filter number+1 on deny incoming all 0.0.0.0 0.0.0.0 255.255.255.255 protocol ICMP Where number is a free filter number between 0 and 17. Exploitation and Public Announcements The vulnerability CSCdr98772 was discovered by several customers. It was also discussed at public forums. PSIRT has received reports that this vulnerability has been exploited in vivo. The vulnerability CSCds23921 was discovered by a customer. The other two vulnerabilities (CSCds59206 and CSCds19142) were discovered during internal testing. The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements of CSCds59206, CSCds19142 and CSCds23921. Status of This Notice: FINAL This is a final 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 does not anticipate issuing updated versions of this notice unless there is some material change in the facts. Should there be a significant change in the facts, Cisco may update this notice. Distribution This notice will be posted on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707/CBOS-multiple.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 *)first-teams@first.org (includes CERT/CC) *)cisco@spot.colorado.edu *)comp.dcom.sys.cisco *)firewalls@lists.gnac.com *)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 1.02000-December-03 21:00 GMT+00 Draft for initial public release Revision 1.12000-December-10 21:00 GMT+00 Updated software availability date, and added instructions on requesting assistance from third-party support organizations in the Obtaining Fixed Software section. Revision 1.22000-December-13 21:00 GMT+00 Updated software availability date, and added instructions for obtaining software. Revision 1.32000-December-19 21:00 GMT+00Removed instructions for temporarily accessing fixed software images; removed text under CSCdr98772 about Web access on Cisco 600 routers. Revision 1.42001-March-19 21:00 GMT+00Updated GA for release 2.3.9; changed status from interim to final. Revision 1.52001-August-08 21:00 GMT+00Updated Workarounds Section 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 2000 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, and include all date and version information. All contents are Copyright © 1992--2001 Cisco Systems Inc. All rights reserved. Important Notices and Privacy Statement. [***** End Cisco Security Advisory Rev. 1.5 *****] _______________________________________________________________________________ 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. 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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. 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