Cisco Warning: VPN Services Face Powerful Password-Spray Onslaught! Quick look


Cisco Warning: VPN Services Face Powerful Password-Spray Onslaught! Quick look

In recent times, organizations have faced a surge in password spray attacks targeting their Remote Access VPN (RAVPN) services. These attacks aim to compromise user accounts by systematically trying common passwords across multiple accounts. Cisco Secure Firewall devices, along with other third-party VPN concentrators, have been affected by these reconnaissance efforts. In this article, we explore the background of password spray attacks and provide actionable recommendations to enhance security.

Background Information

Password spray attacks are not unique to Cisco products; they also impact other VPN services. The consequences can be severe, leading to account lockouts and Denial of Service (DoS)-like conditions. To address this threat, organizations must adopt proactive measures to safeguard their RAVPN services.


1. Enable Logging

Ensure that logging is enabled on your VPN headend (Cisco Secure Firewall ASA or Threat Defense). By monitoring syslog messages, you can detect unusual patterns, such as a high number of rejected authentication attempts. Look out for the following syslog IDs:

  • %ASA-6-113015: AAA user authentication rejected due to the user not being found in the local database.
  • %ASA-6-113005: AAA user authentication rejected for unspecified reasons.
  • %ASA-6-716039: Group <DfltGrpPolicy> User <admin> IP <x.x.x.x> authentication rejected.

2. Secure Default RAVPN Profiles

Review and enhance the default RAVPN profiles. Disable any unnecessary features and ensure that strong authentication mechanisms are in place. Consider using certificate-based authentication to bolster security.

3. Leverage TCP Shun

Implement TCP shun to automatically block IP addresses associated with suspicious activity. This helps prevent repeated authentication attempts from the same source.

4. Control-Plane ACL

Configure a control-plane access control list (ACL) to restrict access to critical services. Limit the exposure of VPN services to only authorized IP addresses.

5. Educate Users

Promote password hygiene among users. Encourage them to choose strong, unique passwords and avoid reusing credentials across different services.


By following these recommendations, organizations can fortify their RAVPN services against password spray attacks. Proactive monitoring, secure configurations, and user education are essential components of a robust defense strategy. Remember that security is a shared responsibility, and staying vigilant is crucial in today’s threat landscape.

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