Cisco IOS Software contains a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service condition. Updates are available.
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.
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.
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.
Cisco has released a security notice at the following link: CVE-2013-5469
Customers are advised to consult Cisco bug ID CSCtz14399 for the most complete list of affected product versions.
An unauthenticated, remote attacker could exploit this vulnerability to cause an affected device to utilize excessive amounts of network and CPU resources, resulting in a denial of service (DoS) condition.
The vulnerability is due to improper closing of established TCP connections.
An unauthenticated, remote attacker could exploit this vulnerability by sending a crafted sequence of TCP ACK and FIN packets to an affected device. Processing these packets could cause the attacker to trigger an ACK storm which may utilize excessive amounts of network and CPU utilization, resulting in a DoS condition.
Administrators are advised to apply the appropriate updates.
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.
Administrators are advised to monitor affected systems.
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 firstname.lastname@example.org for assistance.
The urgency and severity ratings of this alert are not tailored to individual users; users may value alerts differently based upon their network configurations and circumstances. THE ALERT, AND INFORMATION CONTAINED THEREIN, ARE PROVIDED ON AN "AS IS" BASIS AND DO NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE ALERT, AND INFORMATION CONTAINED THEREIN, OR MATERIALS LINKED FROM THE ALERT, IS AT YOUR OWN RISK. INFORMATION IN THIS ALERT AND ANY RELATED COMMUNICATIONS IS BASED ON OUR KNOWLEDGE AT THE TIME OF PUBLICATION AND IS SUBJECT TO CHANGE WITHOUT NOTICE. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE ALERTS AT ANY TIME.