CVE-2021-26109: Fortinet FortiOS

Critical severity, CVSS 9.8. EPSS: 1.9% chance of exploitation in the next 30 days.

An integer overflow or wraparound vulnerability in the memory allocator of SSLVPN in FortiOS before 7.0.1 may allow an unauthenticated attacker to corrupt control data on the heap via specifically crafted requests to SSLVPN, resulting in potentially arbitrary code execution.

Affected products

• Fortinet FortiOS: from 6.0.0, up to and including 6.0.12; from 6.2.0, up to and including 6.2.9; from 6.4.0, up to and including 6.4.5; version 7.0.0 only

Published 2021-12-08. Last modified 2026-06-17.