Cisco Firewall Services Module HTTPS Request Denial of Service Vulnerability

Cisco Firewall Services Module versions prior to 3.1(3.18) contain a vulnerability that could allow an unauthenticated, remote attacker to create a temporary denial of service (DoS) condition.

The vulnerability is due to an error when handling malformed HTTPS requests on devices that are configured to authenticate users before granting network access. An unauthenticated, remote attacker could exploit this vulnerability by attempting to access an external website utilizing the HTTPS protocol. This action could force Cisco Firewall Services Module to reload, resulting in a temporary DoS condition.

Cisco has confirmed this vulnerability with a security advisory and released updated software.

A successful attack allows the attacker to cause the Cisco Firewall Services Module to reload. The device will automatically restart, causing a temporary DoS condition. Repeated attacks could be utilized to create an extended condition. Because the vulnerability only occurs due to an error in handling the HTTPS request itself and not the URL, the attacker would likely have to utilize a custom application to generate the malicious traffic. An attacker is unlikely to be able to leverage a standard web browser to perform an exploit.