Cisco Has A Serious Flaw In ASA That Is Being Actively Exploited

If you run a Cisco Adaptive Security Appliance (ASA), you will want to read this alert from the company. Here’s the TL:DR:

A vulnerability in the remote access VPN feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to conduct a brute force attack in an attempt to identify valid username and password combinations or an authenticated, remote attacker to establish a clientless SSL VPN session with an unauthorized user.

This vulnerability is due to improper separation of authentication, authorization, and accounting (AAA) between the remote access VPN feature and the HTTPS management and site-to-site VPN features. An attacker could exploit this vulnerability by specifying a default connection profile/tunnel group while conducting a brute force attack or while establishing a clientless SSL VPN session using valid credentials. A successful exploit could allow the attacker to achieve one or both of the following:

  • Identify valid credentials that could then be used to establish an unauthorized remote access VPN session.
  • Establish a clientless SSL VPN session (only when running Cisco ASA Software Release 9.16 or earlier).

This flaw has already been tied to ransomware attacks. Making this a today problem for anyone running an ASA box. The Cisco document has mitigations in it that I strongly recommend you take action to implement until Cisco gets around to fixing this.

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