Historical catalog analysis: CISA added this entry on December 16, 2025. The entry reflects catalog information retrieved on August 31, 2026, not a snapshot archived on the inclusion date. Check current vendor guidance before acting.
What the vulnerability is
CVE-2025-59718 is a vulnerability involving the improper verification of cryptographic signatures (CWE-347) within several Fortinet products. This flaw could allow an unauthenticated attacker to bypass the FortiCloud Single Sign-On (SSO) login authentication process by submitting a specially crafted SAML message. A related vulnerability, CVE-2025-59719, pertains to the same underlying problem and is addressed in the same vendor advisory.
Exposure and applicability
This vulnerability affects organizations utilizing FortiCloud SSO for authentication across the following Fortinet product lines:
* FortiOS
* FortiSwitchMaster
* FortiProxy
* FortiWeb
Exposure is highest for environments where these products are configured to rely on SAML-based SSO for administrative or user access, as the vulnerability allows an attacker to circumvent the authentication requirement entirely.
Remediation priorities
Our analysis suggests prioritizing remediation based on the accessibility of the management interfaces and the criticality of the affected assets. We recommend the following priority sequence:
1. Immediate Patching: Apply the updates specified in vendor advisory FG-IR-25-647. Because this vulnerability allows unauthenticated access, patching should be treated as a high-priority event for all internet-facing and internal management interfaces.
2. Comprehensive Update: Ensure that patches for both CVE-2025-59718 and CVE-2025-59719 are applied simultaneously, as they share the same advisory and problem space.
3. Access Restriction: While patching is underway, restricting access to the SSO login interfaces to known, trusted IP ranges could reduce the likelihood of external exploitation.
How to validate remediation
To verify that exposure has been reduced, defenders should move beyond simple version checks. We recommend the following validation approach:
* Version Verification: Confirm that the installed firmware matches or exceeds the patched versions listed in FG-IR-25-647.
* Configuration Audit: Verify that SAML configurations are aligned with current vendor security best practices for signature verification.
* Functional Testing: In a non-production environment, attempt to use an invalid or unsigned SAML assertion to ensure the system correctly rejects the authentication attempt.
Note: A version check alone does not prove that the SSO bypass is fully mitigated if other configuration errors exist in the SAML implementation.
Limits and open questions
It remains unknown whether this vulnerability has been leveraged in known ransomware campaigns. Additionally, while patches are available, the specific cryptographic failure—whether it was a failure to check the signature entirely or a failure to validate the trust chain—is not detailed in the source. Residual risk may remain if organizations use third-party SAML providers with insecure configurations that interact poorly with the patched Fortinet products.
Source and editorial note
CVE-2025-59718: Fortinet Multiple Products Improper Verification of Cryptographic Signature Vulnerability · Source date: December 16, 2025 · Retrieved August 31, 2026.
Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.
Archive date: December 19, 2025. The displayed post date is assigned three days after the source date to organize this retrospective archive; it does not mean this site published the analysis then. First published by this site: September 26, 2026 at 00:12 UTC.
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