Cisco Security Advisory
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AV:N/AC:M/Au:N/C:N/I:N/A:P/E:F/RL:OF/RC:C
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A vulnerability in the TCP stack of Cisco IOS Software could allow an unauthenticated, remote attacker to cause an ACK storm.
The vulnerability is due to improper closing of an established TCP connection. An attacker could exploit this vulnerability by sending a crafted sequence of TCP ACK and FIN packets to an affected device. A successful exploit could allow the attacker to cause an ACK storm resulting in excessive network and CPU utilization.
Cisco has confirmed the vulnerability in a security notice and released software updates.
To exploit this vulnerability, the attacker would need the ability to send a sequence of TCP ACK and FIN packets to the targeted system. To achieve this objective, the attacker may need access to trusted, internal network resources. This access requirement reduces the likelihood of a successful exploit..
Cisco indicates through the CVSS score that functional exploit code exists; however, the code is not known to be publicly available.
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Customers are advised to consult Cisco bug ID CSCtz14399 for the most complete list of affected product versions.
Vulnerable Products
At the time this alert was first published, Cisco IOS Software versions 15.3(3)S6 and prior were vulnerable. Later releases of Cisco IOS Software versions may also be vulnerable.Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by these vulnerabilities.
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Administrators are advised to apply the appropriate updates.
It is critical to prevent unauthorized direct communication to network devices. Restrict network traffic destined for the network infrastructure to protect against reconnaissance and denial of service attacks. For configuration details, see Protecting Your Core: Infrastructure Protection Access Control Lists.
Prevent disruption of communication between devices by reducing the impact of attacks that may directly affect the CPU performance of the individual devices. For control plane hardening best practices, see Cisco Guide to Harden Cisco IOS Devices.
To mitigate denial of service attacks, apply hardware rate limiter features to limit packets that require CPU processing. See vendor documentation for specific configuration instructions. For hardware rate limiting configuration details, see Cisco Catalyst 6500 Denial of Service (DoS) Protection Configuration Guide.
Administrators are advised to monitor affected systems.
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Cisco customers with active contracts should contact their Cisco support team for assistance in upgrading to a software version that includes fixes for this vulnerability. Cisco customers without contracts may contact the Cisco Technical Assistance Center at 1-800-553-2447 or 1-408-526-7209 or via email at tac@cisco.com for assistance.
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The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Show LessVersion Description Section Status Date 1.0 Initial Release NA Final 2013-Sep-03
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