From psirt@cisco.com Tue Dec 5 03:51:11 2000 From: Cisco Systems Product Security Incident Response Team To: cust-security-announce@cisco.com Cc: psirt@cisco.com Date: Mon, 04 Dec 2000 15:30:00 -0400 (EDT) Subject: Cisco Security Advisory: Multiple Vulnerabilities in CBOS -----BEGIN PGP SIGNED MESSAGE----- Multiple Vulnerabilities in CBOS Revision 1.0 For Public Release 2000 December 04 08:00 (GMT +0800) _________________________________________________________________ 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 (ACSII 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. In order 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. Note:Web access on all Cisco 600 routers is disabled by default and must be explicitly enabled. 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 64Kb 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. +===========+================+==============================================+ | | | | | Release | Description or | Availability of Repaired Releases* | | | Platform |==================+===========================+ | | | Patch release** | General Availability (GA) | +===========+================+==================+===========================+ | All | 627, 633, 673 | 2.3.5.015 | | | releases | 675, 677, 678 | 2000-DEC-11 | | +-----------+----------------+------------------+---------------------------+ | 2.3.7.001 | 677i | 2.3.7.002 | | | | | 2000-DEC-11 | | +-----------+----------------+------------------+---------------------------+ | All | All platforms | | 2.3.9 | | releases | | | 2001-JAN | +-----------+----------------+------------------+---------------------------+ | All | All platforms | | 2.4.1 | | releases | | | 2000-DEC-11 | +===========+================+==================+===========================+ | 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 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 remote 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 remote disable 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 remote disable 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: INTERIM This is an interim notice. Cisco expects the contents of this report to change. The reader is warned that this notice may contain inaccurate or incomplete information. 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 anticipates issuing monthly updates of this notice until it reaches final status. 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 1.0 2000-December-03 21:00 GMT+00 Draft for initial public release 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. 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