Cyber Security Threat Summary:
“Hundreds of thousands of FortiGate firewalls are vulnerable to a critical security issue identified as CVE-2023-27997, almost a month after Fortinet released an update that addresses the problem. The vulnerability is a remote code execution with a severity score of 9.8 out of 10 resulting from a heap-based buffer overflow problem in FortiOS, the operating system that connects all Fortinet networking components to integrate them in the vendor's Security Fabric platform” (Bleeping Computer, 2023).

The vulnerability allows an unauthenticated attacker to execute remote commands on vulnerable devices with SSL VPN interfaces exposed on the Internet. Exploitation against the vulnerability likely began in mid-June 2023, Fortinet addressed the vulnerability on June 11 before disclosing it publicly, by releasing FortiOS firmware versions 6.0.17, 6.2.15, 6.4.13, 7.0.12, and 7.2.5.

Security Officer Comments:
Researchers are urging customers to patch, as more than 300,000 FortiGate firewalls still appear vulnerable and publicly exposed via Shodan searches. Bishop Fox researchers used the Shodan search engine to find devices that responded in a way that indicated an exposed SSL VPN interface. They achieved this by searching for appliances that returned a specific HTTP response header. They filtered the results to those that redirected to ‘/remote/login,’ a clear indication of an exposed SSL VPN interface.

“The query showed 489,337 devices but not all of them were vulnerable to CVE-2023-27997, also referred to as Xortigate. Investigating further, the researchers discovered that 153,414 of the discovered appliances had been updated to a safe FortiOS version” (Bleeping Computer, 2023). This means that roughly 335,900 of the FortiGate firewalls reachable over the web are vulnerable to attacks, a number that is significantly higher than the 250,000 recent estimation based on other, less accurate queries, Bishop Fox researchers say.

Even more concerning, Bishop Fox researchers found that some of the exposed FortiGate devices had not received an update in the past eight years, with many still running FortiOS 6, which has reached end of support last year on September 29th. These devices are vulnerable to several critical-severity flaws that have proof-of-concept exploit code publicly available.

Suggested Correction(s):
To demonstrate that CVE-2023-27997 can be used to execute code remotely on vulnerable devices, Bishop Fox created an exploit that allows "smashes the heap, connects back to an attacker-controlled server, downloads a BusyBox binary, and opens an interactive shell."

Users should update their FortiGate firewalls as soon as possible. Attacks against devices like these that sit on the edge of a network have been increasing as of late, especially from sophisticated Chinese nation-state actors.

Link(s):
https://www.bleepingcomputer.com/