Cisco Adaptive Security Appliance Software and Firewall Services Module Software contain a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service condition. Updates are available.
A vulnerability in the implementation of the Secure Shell (SSH) function could allow an unauthenticated, remote attacker to deny SSH management access to legitimate users.
The vulnerability is due to improper implementation of the logic to terminate SSH sessions. An attacker could exploit this vulnerability by starting an SSH session to the affected system. This vulnerability affects both SSHv1 and v2. An exploit could allow the attacker to deny SSH management access to legitimate users. The attacker can deny the access for 60 seconds, and then the affected system will release the resource and users will be able to use the SSH service again. However, repeated exploitation may lead to a denial of service condition.
Cisco has confirmed the vulnerability in a security notice and software updates are available.
At the time this alert was first published, the following versions of Cisco products were vulnerable. Later versions of Cisco products may also be affected.
Cisco ASA Software versions 8.4.6 and prior
Cisco FWSM versions 4.1.7 and prior
An attacker can only deny access to a targeted system for 60 seconds, which then the affected system will release the resource to allow legitimate users SSH access again. However, repeated exploitation could lead to a sustained DoS condition.
Customers are advised to review the bug report in the vendor announcements section for a current list of affected versions.
Cisco indicates through the CVSS score that functional exploit code exists; however, the code is not known to be publicly available.
An unauthenticated, remote attacker could exploit this vulnerability to deny SSH management access to legitimate users, resulting in a denial of service (DoS) condition.
The vulnerability is due to improper implementation of the SSH function used by the affected software. The affected software fails to properly terminate SSH sessions.
An unauthenticated, remote attacker could exploit this vulnerability by starting an SSH session to an affected system. Successful exploitation could allow the attacker to deny SSH management access to legitimate users, resulting in a DoS condition.
Administrators are advised to apply the appropriate updates.
Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.
Administrators are advised to allow only privileged users to access administration or management systems.
Administrators may consider using the HTTPS management interface instead of the SSH management access.
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 e-mail at email@example.com 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.