Cisco 1800 Series Integrated Services Routers contain a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service condition. Updates are not available.
Cisco 1800 Series Integrated Services Routers (ISR) contain a vulnerability in the hardware entropy collection module when the Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI) is configured and connected to a public switched network. This could allow an attacker with knowledge of the ISDN phone number of the affected device to trigger a denial of service (DoS) condition.
The vulnerability is due to an interrupt timer collision that causes the hardware encryption module to enter a corrupted state, causing the device to become unresponsive. An attacker would need to perform the attack exactly when the device polls the hardware encryption module to perform entropy collection.
The affected devices have reached the End of Software Maintenance milestone. Fixed software will not be released.
Cisco has confirmed the vulnerability in a security notice; however, software updates are not available.
At the time this alert was first published, Cisco IOS Software Releases 15.1(4)M2 or later were vulnerable. Later releases may also be vulnerable.
To exploit this vulnerability, an attacker must obtain additional knowledge of the targeted device, such as whether ISDN BRI is configured and connected to an active switched network and whether a service that requires encryption entropy collection is enabled. The additional knowledge requirement may decrease the likelihood of a successful exploit.
Cisco has released a security notice at the following link: CVE-2014-3347
Customers are advised to consult Cisco bug ID CSCul77897 for a complete list of affected product versions.
An unauthenticated, remote attacker could exploit this vulnerability to cause an affected device to become unresponsive, resulting in a DoS condition.
The vulnerability is due to an interrupt timer collision that causes the hardware encryption module to enter a corrupted state when the ISDN BRI on an affected device is configured and connected to a public switch network, causing the device to become unresponsive.
An attacker with knowledge of the ISDN phone number of the affected device could exploit this vulnerability to trigger a DoS condition.
Administrators are advised to downgrade to a version of Cisco IOS Software that does not use hardware entropy collection.
Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.
Administrators are advised to monitor affected systems.
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.