data breaches
From VPN to FortiManager: Attack Pattern Suggests Preparation for New Exploit
Cyber threat actors orchestrated a massive, two-wave brute-force assault on Fortinet SSL VPNs, shifting mid-campaign to FortiManager—raising alarm as such patterns often precede critical CVE disclosures.
A Storm on the Horizon
In the digital realm, a flurry of failed login attempts might seem mundane—until 780 unique IPs suddenly focus on Fortinet’s VPN infrastructure. That’s precisely the scale and precision of the blitz observed by GreyNoise on August 3, signaling a dangerous prelude to potential zero-day disclosures.
Two Waves of Attack, One Malicious Strategy
Cybersecurity firm GreyNoise documented an unprecedented spike in brute-force attempts against Fortinet SSL VPN infrastructure. More than 780 distinct IP addresses were involved in a single day—the largest surge seen in months .
The attack unfolded in two distinct phases:
- Wave One: A persistent brute-force effort using a consistent TCP signature, targeting FortiOS SSL VPN systems.
- Wave Two (from August 5): A sudden, more powerful burst employing a new TCP and client signature, redirecting focus toward FortiManager platforms .
GreyNoise noted this progression as a strategic shift—possibly the same attacker infrastructure pivoting to more sensitive management interfaces.
Technical Breadcrumbs Reveal Residential Links
Analysis uncovered several IP addresses such as 31.206.51.194 and 23.120.100.230, linked to the campaign. Intriguingly, some traffic originated from a residential ISP block, pointing to compromised home routers or proxy abuse.
A Warning Sign for Imminent Vulnerabilities
History shows these brute-force spikes are rarely random. GreyNoise’s research indicates that 80% of similar surges have preceded a new CVE disclosure affecting the same vendor within six weeks.
Human Impact: Why This Matters
For IT teams and executives in affected sectors—finance, healthcare, government—the implications are dire:
- A successful brute-force breach could grant attackers unauthorized access to VPN sessions or administrative interfaces.
- If paired with an undisclosed vulnerability, the result could be full device compromise, lateral movement, or data exfiltration.
- The pattern of shifting targets—from VPN to FortiManager—underscores the potential for deeper system penetration.
Expert Voices
“This was not opportunistic — it was focused activity,” said GreyNoise, underscoring the precision and intent behind the attack wave .
How to Protect Your Environment
Fortify VPN Protection
- Employ rate limiting and account lockouts after failed login attempts.
- Layer on multi-factor authentication (MFA) as a mandatory requirement.
Harden FortiManager Access
- Restrict access via IP whitelisting or VPN-only tunnels.
- Monitor for unusual access patterns or spikes.
Block Malicious Traffic
- Share and implement the Fortinet SSL-VPN Bruteforcer tag indicators from GreyNoise on your firewalls and SIEM.
- Consider using dynamic IP blocklists to stay ahead of evolving threats.
Stay Ahead of Zero-Day Risks
- Treat this brute-force wave as an early warning. Expedite patching of known Fortinet vulnerabilities such as CVE‑2024‑21762, CVE‑2023‑27997, and CVE‑2022‑42475.
Good cyber hygiene—prompt patching, monitoring, and access control—remains your best defense against evolving threats.
Source: The Hacker News