Cisco Talos would like to acknowledge Brandon White of Cisco Talos and Phillip Schafer, Mike Moran, and Becca Lynch of the Duo Security Research team for their research that led to the identification of these attacks.

Cisco Talos is actively monitoring a global increase in brute-force attacks against a variety of targets, including Virtual Private Network (VPN) services, web application authentication interfaces and SSH services since at least March 18, 2024.  

These attacks all appear to be originating from TOR exit nodes and a range of other anonymizing tunnels and proxies.  

Depending on the target environment, successful attacks of this type may lead to unauthorized network access, account lockouts, or denial-of-service conditions. The traffic related to these attacks has increased with time and is likely to continue to rise. Known affected services are listed below. However, additional services may be impacted by these attacks. 

• Cisco Secure Firewall VPN 
• Checkpoint VPN  
• Fortinet VPN  
• SonicWall VPN  
• RD Web Services 
• Miktrotik 
• Draytek 
• Ubiquiti 

The brute-forcing attempts use generic usernames and valid usernames for specific organizations. The targeting of these attacks appears to be indiscriminate and not directed at a particular region or industry. The source IP addresses for this traffic are commonly associated with proxy services, which include, but are not limited to:  

• TOR   
• VPN Gate  
• IPIDEA Proxy  
• BigMama Proxy  
• Space Proxies  
• Nexus Proxy  
• Proxy Rack 

The list provided above is non-exhaustive, as additional services may be utilized by threat actors.  

Due to the significant increase and high volume of traffic, we have added the known associated IP addresses to our blocklist. It is important to note that the source IP addresses for this traffic are likely to change.

Guidance 

As these attacks target a variety of VPN services, mitigations will vary depending on the affected service. For Cisco remote access VPN services, guidance and recommendation can be found in a recent Cisco support blog:  

Best Practices Against Password Spray Attacks Impacting Remote Access VPN Services 

IOCs 

We are including the usernames and passwords used in these attacks in the IOCs for awareness. IP addresses and credentials associated with these attacks can be found in our GitHub repository here.