Critical FortiGate 100F SSL-VPN Vulnerability Exploited by | Jun 24, 2025 | Articles, External Pentesting Write ups

Reading Time: 3 Minutes

Introduction
While automated tools are useful for maintaining baseline security, they often miss sophisticated, multi-layered vulnerabilities that require a manual, strategic approach to uncover. At Black Hat Ethical Hacking (BHEH), our Red Team employs advanced manual testing, real-world attack simulations, and in-depth system analysis to uncover vulnerabilities that automated methods often overlook. This process highlights the importance of human expertise and creativity in identifying and exploiting complex weaknesses that could compromise even well-protected systems.
 

Executive Summary
During an external penetration test, our red team identified a critical vulnerability on FortiGate 100F firewall appliances. The issue is CVE-2022-42475 – a heap-based buffer overflow in FortiOS’s SSL-VPN service that allows remote, unauthenticated code execution. The affected FortiGate devices were found exposed on non-standard ports (TCP 4433 and 32015) through careful reconnaissance, including the use of Shodan for internet-wide scanning. An attacker exploiting this flaw could fully compromise the firewall, bypassing perimeter defenses and gaining potential access to internal networks. Given the vulnerability’s critical severity (CVSS 3.1 base score 9.8) and known exploitation by advanced threat actors in the wild, this finding poses a Critical risk to the organization’s security.
Security Lesson Learned: Critical perimeter systems like firewalls must be continuously patched, actively monitored, and never assumed hidden—obscurity is not a defense.
The following report de...