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Fortinet Releases Guidance to Address Ongoing Exploitation of Authentication Bypass Vulnerability CVE-2026-24858

Newly disclosed vulnerability Common Vulnerabilities and Exposures (CVE)-2026-24858 [Common Weakness Enumeration (CWE)-288: Authentication Bypass Using an Alternate Path or Channel] allows malicious actors with a FortiCloud account and a registered device to log in to separate devices registered to other users in FortiOS, FortiManager, FortiWeb, FortiProxy, and FortiAnalyzer, if FortiCloud single sign on (SSO) is enabled on devices.1

Users are vulnerable to CVE-2026-24858 even if they updated Fortinet devices to address previously disclosed FortiCloud SSO bypass vulnerabilities CVE-2025-59718 and CVE-2025-59719 [CWE-347: Improper Verification of Cryptographic Signature]2 CVE-2025-59718 and CVE-2025-59719 affect FortiOS, FortiWeb, FortiProxy, and FortiSwitch Manager, and allow malicious actors to bypass the SSO login authentication via a crafted Security Assertion Markup Language (SAML) message.3  On Fortinet devices that had been fully upgraded to the latest release addressing CVE-2025-59718 and CVE-2025-59719 the time of CVE-2026-24858 exploitation, Fortinet observed the following malicious activity: