Fortinet confirmed that a December patch failed to fully secure its FortiCloud single sign-on system, allowing attackers to access devices with the supposed fix. New attack methods have been identified, prompting Fortinet to investigate further and advise customers to monitor for unusual login activity.

Fortinet disclosed a new zero-day vulnerability, CVE-2026-24858, which allows attackers to exploit the FortiCloud single sign-on feature for unauthorized logins. This critical flaw has a CVSS score of 9.8 and affects multiple Fortinet products, prompting the company to temporarily disable SSO authentication to mitigate ongoing attacks.