SB2026012392 - FortiCloud SSO login authentication bypass in Fortinet products

Description

This security bulletin contains information about 1 security vulnerability.

1) Improper verification of cryptographic signature (CVE-ID: CVE-2026-24858)

The vulnerability allows a remote attacker to bypass SSO authentication.

The vulnerability exists due to improper verification of cryptographic signature when handling SAML messages. A remote non-authenticated attacker can bypass the FortiCloud SSO login authentication via a crafted SAML message. 

Successful exploitation of the vulnerability requires that the FortiCloud SSO feature is enabled on the device. However, when an administrator registers the device to FortiCare from the device's GUI, unless the administrator disables the toggle switch "Allow administrative login using FortiCloud SSO" in the registration page, FortiCloud SSO login is enabled upon registration.

This vulnerability exists due to incomplete fix for #VU119694 (CVE-2025-59718) and #VU119696 (CVE-2025-59719).

Note, the vulnerability is being actively exploited in the wild.

Remediation

Install update from vendor's website.

References

• https://www.fortinet.com/blog/psirt-blogs/analysis-of-sso-abuse-on-fortios
• https://www.fortiguard.com/psirt/FG-IR-26-060