Hackers are exploiting a new Fortinet firewall bug to breach company networks

Security researchers say malicious hackers have been exploiting a newly discovered vulnerability in Fortinet firewalls to break into corporate and enterprise networks.

In an advisory published Tuesday, security product maker Fortinet confirmed that a critical-rated vulnerability in its FortiGate firewalls, tracked as CVE-2024-55591, is “being exploited in the wild.” 

Fortinet made patches available, but security researchers have warned that hackers have been mass-exploiting the vulnerability as a zero-day — meaning before Fortinet was aware of the vulnerability and made fixes available — since December.

This is the latest example of hackers exploiting a vulnerability in a popular enterprise security product designed to protect corporate networks from intruders. News of the Fortinet bug lands days after it was revealed that attackers are exploiting a separate zero-day flaw in Ivanti VPN servers that allows access to customers’ networks.

Cybersecurity company Arctic Wolf said in a blog post last week that its researchers observed a recent “mass exploitation” campaign affecting Fortinet FortiGate firewall devices with management interfaces exposed to the public internet.

Stefan Hostetler, lead threat intelligence researcher at Arctic Wolf, confirmed to TechCrunch that this observed exploitation is linked to the newly confirmed CVE-2024-55591 vulnerability in Fortinet firewalls. 

Hostetler told TechCrunch that Arctic Wolf had “observed a cluster of intrusions affecting Fortinet devices in the tens,” but notes that this only represents a “limited sample compared to the total actual number of devices that were likely affected.”

“The evidence points to an effort to exploit a large number of devices within a narrow time frame,” added Hostetler.

When reached by TechCrunch, Fortinet spokesperson Tiffany Curci declined to say how many Fortinet customers were compromised as a result of this hacking campaign, but said that the company was “proactively communicating with customers.”

It’s also unclear who is behind the attacks on Fortinet firewalls, but cybersecurity researcher Kevin Beaumont writes on Mastodon that the vulnerability is “under exploitation by a ransomware operator.” 

Hostetler said that ransomware attacks exploiting the bug are “not off the table,” noting that in previous research, Arctic Fox “observed affiliates of ransomware groups such as Akira and Fog using some of the same network providers to establish VPN connectivity.”

In a brief statement on Tuesday, U.S. cybersecurity CISA urged Fortinet customers to update any affected devices.

In September, Fortinet disclosed a breach involving customer data after an attacker accessed “a limited number of files” stored on a third-party shared cloud drive belonging to the organization.