Voor degenen die geen cert advisories binnen krijgen. ----- Forwarded message from CERT Advisory <cert-advisory at cert.org> ----- From: CERT Advisory <cert-advisory@cert.org> To: cert-advisory at cert.org Date: Thu, 17 Jul 2003 00:10:17 -0400 Subject: CERT Advisory CA-2003-15 Cisco IOS Interface Blocked by IPv4 Packet Organization: CERT(R) Coordination Center - +1 412-268-7090 List-Help: <http://www.cert.org/>, <mailto:Majordomo at cert.org?body=help> List-Subscribe: <mailto:Majordomo at cert.org?body=subscribe%20cert-advisory> List-Unsubscribe: <mailto:Majordomo at cert.org?body=unsubscribe%20cert-advisory> List-Post: NO (posting not allowed on this list) List-Owner: <mailto:cert-advisory-owner at cert.org> List-Archive: <http://www.cert.org/> Precedence: list CERT Advisory CA-2003-15 Cisco IOS Interface Blocked by IPv4 Packet Original release date: July 16, 2003 Last revised: -- Source: CERT/CC A complete revision history can be found at the end of this file. Systems Affected * All Cisco devices running Cisco IOS software and configured to process Internet Protocol version 4 (IPv4) packets Overview A vulnerability in many versions of Cisco IOS could allow an intruder to execute a denial-of-service attack against a vulnerable device. I. Description Cisco IOS is a very widely deployed network operating system. A vulnerability in IOS could allow an intruder to execute a denial-of-service attack against an affected device. Cisco has published an advisory on this topic, available at http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtml We strongly encourage sites using IOS to read this document and take appropriate action. The CERT/CC is tracking this issue as VU#411332. This reference number corresponds to CVE candidate CAN-2003-0567. II. Impact By sending specially crafted IPv4 packets to an interface on a vulnerable device, an intruder can cause the device to stop processing packets destined to that interface. Quoting from Cisco's advisory: "A device receiving these specifically crafted IPv4 packets will force the inbound interface to stop processing traffic. The device may stop processing packets destined to the router, including routing protocol packets and ARP packets. No alarms will be triggered, nor will the router reload to correct itself. This issue can affect all Cisco devices running Cisco IOS software. This vulnerability may be exercised repeatedly resulting in loss of availability until a workaround has been applied or the device has been upgraded to a fixed version of code." III. Solution Apply a patch from Cisco Apply a patch as described in Cisco's Advisory. Until a patch can be applied, you can mitigate the risks presented by this vulnerability by judicious use of access control lists (ACLs). The correct use of ACLs depends of your network topology. Additionally, ACLs may degrade performace on some systems. We recommend reviewing the following before applying ACLs http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtml#workaro... http://www.cisco.com/warp/public/707/racl.html http://www.cisco.com/warp/public/707/iacl.html _________________________________________________________________ The CERT Coordination Center thanks Cisco Systems of for notifying us about this problem and for helping us to construct this advisory. _________________________________________________________________ Feedback about this advisory may be directed to the author, Shawn Hernan ______________________________________________________________________ This document is available from: http://www.cert.org/advisories/CA-2003-15.html ______________________________________________________________________ CERT/CC Contact Information Email: cert at cert.org Phone: +1 412-268-7090 (24-hour hotline) Fax: +1 412-268-6989 Postal address: CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 U.S.A. CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) / EDT(GMT-4) Monday through Friday; they are on call for emergencies during other hours, on U.S. holidays, and on weekends. Using encryption We strongly urge you to encrypt sensitive information sent by email. Our public PGP key is available from http://www.cert.org/CERT_PGP.key If you prefer to use DES, please call the CERT hotline for more information. Getting security information CERT publications and other security information are available from our web site http://www.cert.org/ To subscribe to the CERT mailing list for advisories and bulletins, send email to majordomo at cert.org. Please include in the body of your message subscribe cert-advisory * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office. ______________________________________________________________________ NO WARRANTY Any material furnished by Carnegie Mellon University and the Software Engineering Institute is furnished on an "as is" basis. Carnegie Mellon University makes no warranties of any kind, either expressed or implied as to any matter including, but not limited to, warranty of fitness for a particular purpose or merchantability, exclusivity or results obtained from use of the material. Carnegie Mellon University does not make any warranty of any kind with respect to freedom from patent, trademark, or copyright infringement. _________________________________________________________________ Conditions for use, disclaimers, and sponsorship information Copyright 2003 Carnegie Mellon University. Revision History July 16, 2003: Initial release ----- End forwarded message ----- -- Tycho Eggen (Unix|Network|Social) Engineer tycho at e-dude.org +31 6 41 824 855 "Don't worry over what other people are thinking about you." "They're too busy worrying over what you are thinking about them."