Cisco Warns of Password Spraying Attacks Exploiting VPN Services

Password spraying is a technique hackers often take advantage of because it enables them to gain unauthorized access to many accounts or systems. They can potentially compromise many targets with little difficulty by using the same passwords for several accounts. 

It is a low-risk and high-reward attack method that the threat actors use while trying to get into networks or steal private information as password spraying defeats account lockout mechanisms.

Recently, cybersecurity researchers at Cisco warned of password-spraying attacks that are actively targeting VPN services.

Password Spraying Attacks Exploiting VPN Services

Cisco acknowledged reports of password spraying attacks targeting RAVPN services, including its own products and third-party VPN concentrators, as noted by Talos.


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The attacks can lock accounts, leading to DoS-like conditions, depending on the environment. While this activity seems related to reconnaissance efforts.

Since VPNs provide remote access to internal networks, which makes them attractive targets for gaining unauthorized entry. Password spraying allows hackers to test many common passwords across numerous accounts without triggering account lockouts.

Successful VPN compromise can grant access to sensitive data and systems within the organization’s network. Threat actors can leverage compromised VPN accounts for further lateral movement and escalation of privileges within the breached environment.

VPN services often employ weak or reused passwords, increasing the chances of success for password spraying attacks.


Here below we have mentioned all the recommendations offered by the cybersecurity analysts at Cisco:-

  • Enable Logging
  • Secure Default Remote Access VPN Profiles
  • Leverage TCP shun
  • Configure Control-plance ACL
  • Use Certificate-based authentication for RAVPN


  • Unable to establish VPN connections with Cisco Secure Client (AnyConnect) when Firewall Posture (HostScan) is enabled

Users attempting VPN connections with Cisco Secure Client encounter an error about Cisco Secure Desktop not being installed and this prevents the successful connections. 

Cisco secure client (Source – Cisco)

This symptom seems a side effect of the DoS-like attacks but further investigation still continues.

  • Unusual Amount of Authentication Requests

The Cisco ASA or FTD VPN headends exhibit the symptoms of password spraying, with millions of rejected authentication attempts visible in the “syslogs.”

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Gurubaran is a co-founder of Cyber Security News and GBHackers On Security. He has 10+ years of experience as a Security Consultant, Editor, and Analyst in cybersecurity, technology, and communications.