Ethical Hacking News
A recent spike in brute-force attacks targeting Fortinet SSL VPNs has raised concerns about potential zero-day vulnerabilities, prompting experts to urge defenders to strengthen security measures and block malicious IP addresses.
Recent surge in brute-force attacks targeted Fortinet SSL VPNs. Attacks shifted from Fortinet SSL VPNs to FortiManager devices, raising concerns about potential zero-day vulnerabilities. The attacks are believed to be related to upcoming security patches or updates, with spikes in activity often preceding vulnerability disclosures. The attackers used sophisticated tactics, including JA4+ fingerprint analysis and retooling of existing infrastructure, suggesting a high level of planning and sophistication. Defenders are advised to block malicious IP addresses, increase login protection on Fortinet devices, and harden external access to restrict access to trusted IP ranges and VPNs.
Fortinet's SSL VPNs have long been a popular choice among organizations looking to provide secure access to their networks. However, like any other security solution, they are not immune to the threats posed by determined attackers. Recently, a surge in brute-force attacks targeted Fortinet SSL VPNs, followed by a shift in targeting to FortiManager devices, has raised concerns about potential zero-day vulnerabilities.
The campaign, detected by threat monitoring platform GreyNoise, manifested in two waves, on August 3 and August 5, with the second wave pivoting to FortiManager targeting with a different TCP signature. This deliberate shift in targeting has historically preceded new vulnerability disclosures, suggesting that the attacks may be related to upcoming security patches or updates.
GreyNoise notes that such spikes in activity often precede the disclosure of new vulnerabilities affecting the same vendor — most within six weeks. In fact, GreyNoise found that spikes in activity triggering this exact tag are significantly correlated with future disclosed vulnerabilities in Fortinet products. This correlation has led experts to warn defenders not to dismiss these spikes as failed attempts to exploit old, patched flaws but rather to treat them as potential precursors to zero-day disclosure.
The attackers' tactics, use of JA4+ fingerprint analysis for network fingerprinting, and the reuse or retooling of existing infrastructure, suggest a level of sophistication and planning that goes beyond mere script kiddie attacks. The fact that the IP addresses associated with this activity are evolving over time and are likely associated with an adaptive testing framework adds to the complexity of the threat.
Defenders are advised to block the listed IPs, increase login protection on Fortinet devices, and harden external access where possible, restricting access only to trusted IP ranges and VPNs. The sheer volume of attacks and the level of sophistication involved in these campaigns underscore the need for proactive security measures to detect and respond to potential threats.
In conclusion, the recent spike in brute-force attacks targeting Fortinet SSL VPNs serves as a reminder that no organization is immune to cyber threats. As we approach new vulnerability disclosures from Fortinet, defenders must remain vigilant and take steps to strengthen their network security. By blocking malicious IP addresses, increasing login protection, and hardening external access, organizations can reduce the risk of these types of attacks and protect their sensitive data.
The impact of this campaign should not be underestimated, as it highlights the growing sophistication of cyber threats and the need for proactive defense measures. As we continue to navigate the complex landscape of network security, it is essential that defenders remain informed and adapt quickly to emerging threats like the recent Fortinet SSL VPN brute-force attacks.
Related Information:
https://www.ethicalhackingnews.com/articles/A-Deliberate-Shift-in-Brute-Force-Attacks-What-It-Means-for-Your-Fortinet-Network-Security-ehn.shtml
Published: Wed Aug 13 11:49:50 2025 by llama3.2 3B Q4_K_M
