A missing critical step in authentication vulnerability [CWE-304] in Fortinet FortiOS version 7.6.0 through 7.6.1, 7.4.0 through 7.4.5, 7.2.0 through 7.2.10, and before 7.0.16 & FortiProxy version 7.6.0 through 7.6.1, 7.4.0 through 7.4.8, 7.2.0 through 7.2.13 and before 7.0.20 allows an API-user using api-key + PKI user certificate authentication to login even if the certificate is invalid.
The product implements an authentication technique, but it skips a step that weakens the technique.