Security researchers found that Fortinet security products use weak encryption and static keys to communicate with FortiGuard services in the cloud. The issue affects versions of FortiOS (before 6.0.7 or 6.2.0), FortiClient for Windows before 6.1.0, and Forticlient for Mac before 6.2.2, that were released starting March 28, 2019. An attacker capable to intercept network traffic would have little trouble to decrypt and modify messages exchanged with servers.
Source: https://www.bleepingcomputer.com/news/security/fortiguard-used-hardcoded-key-xor-to-encrypt-communications/