Threat Report

COORDINATED BRUTE FORCE CAMPAIGN TARGETS FORTINET SSL VPN A coordinated brute force campaign targeting Fortinet SSL VPNs was observed on August 3, with over 780 unique IPs triggering the Fortinet SSL VPN Bruteforcer tag.

Threat Overview

On August 3, 2025, a significant spike in brute-force traffic targeting Fortinet SSL VPNs was detected. This activity involved over 780 unique IP addresses that triggered the Fortinet SSL VPN Bruteforcer tag. The campaign was deliberate and precise, focusing primarily on FortiOS. Two distinct waves of attacks were identified: a long-running set of brute-force activities and a sudden burst beginning on August 5. The second wave shifted its focus from targeting FortiOS to FortiManager – FGFM profiles.

Historical data analysis suggests that the origin of these attacks could be residential IPs or proxies, indicating an attempt by threat actors to mask their true locations. This evolving attack pattern and potential reuse of tooling are concerning trends observed in this campaign. Research indicates that such spikes often precede new vulnerability disclosures within six weeks.

Detailed Analysis

The brute-force campaign targeting Fortinet SSL VPNs is a sophisticated operation designed to exploit vulnerabilities in the FortiOS and FortiManager systems. The use of over 780 unique IPs suggests a well-coordinated effort by threat actors, likely aiming to bypass traditional security measures.

The first wave of attacks began on August 3 and involved sustained brute-force attempts against FortiOS devices. These attacks were methodical and targeted specific vulnerabilities within the Fortinet SSL VPN infrastructure. The second wave, starting on August 5, shifted its focus to FortiManager – FGFM profiles, indicating an adaptable threat actor capable of adjusting their tactics based on initial observations.

The use of residential IPs or proxies adds another layer of complexity to this campaign. By masking their true locations, threat actors can evade detection and make it more challenging for defenders to trace the origin of these attacks. This tactic also allows them to blend in with legitimate traffic, making it harder for security tools to differentiate between malicious and benign activities.

The evolving nature of this campaign suggests that threat actors are continuously refining their techniques and tooling. The shift from FortiOS to FortiManager – FGFM profiles indicates a deep understanding of the target environment and an ability to exploit multiple vulnerabilities within the same ecosystem.

Operational Security Measures

While the campaign demonstrates advanced tactics, there are still indicators that can help security analysts detect and mitigate these threats. The use of residential IPs or proxies, while effective in masking origins, can sometimes leave traces that can be identified through thorough analysis. Additionally, the reuse of tooling may result in distinctive patterns that can be flagged by intrusion detection systems.

Recommendations for Mitigation

Defenders are advised to take several proactive measures to mitigate the risks associated with this campaign:

• Monitor and Block Malicious IPs: Use tools like GreyNoise to search for and block malicious IPs associated with this campaign. Regularly update your IP blacklists based on the latest threat intelligence.
• Enhance Authentication Mechanisms: Implement multi-factor authentication (MFA) for all VPN access points. This adds an extra layer of security, making it more difficult for attackers to gain unauthorized access.
• Regular Security Audits: Conduct regular security audits and vulnerability assessments on your Fortinet SSL VPN infrastructure. Ensure that all systems are patched and up-to-date with the latest security updates.
• Network Segmentation: Implement network segmentation to limit the lateral movement of attackers within your network. This can help contain potential breaches and prevent widespread damage.
• Intrusion Detection Systems (IDS): Deploy IDS to monitor network traffic for signs of malicious activity. Configure your IDS to alert on suspicious patterns associated with brute-force attacks.
• Endpoint Protection: Ensure that all endpoints accessing the VPN are protected by robust endpoint security solutions. This includes antivirus software, firewalls, and regular system updates.
• Security Awareness Training: Provide ongoing security awareness training to employees. Educate them on recognizing phishing attempts, using strong passwords, and reporting suspicious activities.

By implementing these recommendations, organizations can significantly enhance their defenses against coordinated brute-force campaigns targeting Fortinet SSL VPNs.