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CVE-2022-42475: Fortinet Patches Zero-Day in FortiOS SSL VPNs



Fortinet has patched a zero-day buffer overflow in FortiOS that could lead to remote code execution. There has been a report of active exploitation and organisations should patch urgently.


On December 9 Olympe Cyberdefense published a brief summary of a vulnerability affecting several versions of Fortinet FortiOS used in its FortiGate secure socket layer virtual private network (SSL VPN) and firewall products.

Fortinet followed up on December 12 with an advisory which elaborated that the vulnerability has been observed under exploitation. Fortinet’s language implies this exploitation was limited in scope, specifying “an instance.” It is unclear whether Fortinet observed this exploitation directly or if it was reported to them by the researchers.


CVE-2022-42475 is a heap-based buffer overflow in several versions of ForiOS that received a CVSSv3 score of 9.3. A remote, unauthenticated attacker could exploit this vulnerability with a specially crafted request and gain code execution. The blog from Olympe Cyberdefense goes further, stating attackers could gain “full control.”

Threat actors have been leveragingvulnerabilities in Fortinet SSL VPNs in attacks for several years to the extent that the Federal Bureau of Investigation and Cybersecurity and Infrastructure Security Agency issued a dedicated advisory to these flaws and their exploitation in 2021. Given that this vulnerability has already been exploited, organizations should patch CVE-2022-42475 immediately.


According to Fortinet’s advisory, the following are the affected versions of FortiOS and the relevant fixed versions:

Fortinet’s advisory also includes indicators of compromise (IoC) for the observed exploitation of this flaw. The advisory from Fortinet recommends reviewing systems for these IoCs as does the blog from Olympe Cyberdefense.

Identifying Affected Systems

A list of Tenable plugins to identify this vulnerability can be found here. This link uses a search filter to ensure that all matching plugin coverage will appear as it is released. In addition, plugin ID 73522 can be used to identify Fortinet devices in your network. A Tenable audit with best practices for Fortigate FortiOS is also available here which can help with security hardening.



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