Cisco Adaptive Security Appliance Message Authentication Code Checking Vulnerability

A vulnerability in the Transport Layer Security (TLS) code on the Cisco Adaptive Security Appliance (ASA) could allow an unauthenticated, remote attacker to modify the contents of an encrypted TLS packet without detection of the modifications.

The vulnerability is due to an error on the firmware of the Cavium Networks cryptographic module. Due to this vulnerability, the message authentication code (MAC) on a TLS packet is not being checked. An attacker could exploit this vulnerability by intercepting encrypted packets in transit and modifying their contents. Such packets would be decrypted by the ASA, but the modification would not be detected.

Cisco has confirmed the vulnerability and released software updates.

To exploit this vulnerability, the attacker may need to be in a position to perform a man-in-the-middle attack and be able to intercept encrypted TLS packets in transit from a targeted device, making exploitation more difficult in environments that restrict network access from untrusted sources.

A successful exploit of this vulnerability does not allow an attacker to decrypt the packets in transit or obtain information about the session keys being used for the TLS connection.

Cisco would like to that Mr. Yngve Pettersen from TLS Prober Labs for reporting this vulnerability.