Improper Cryptographic Signature Verification in Fortinet FortiOS, FortiSwitchMaster, FortiProxy, and FortiWeb (CVE‑2025‑59718) Enables SSO Bypass
What It Is — Fortinet’s FortiOS, FortiSwitchMaster, FortiProxy and FortiWeb contain an improper verification of cryptographic signatures that can allow an unauthenticated attacker to bypass FortiCloud SSO login by sending a crafted SAML assertion. The flaw is tracked as CVE‑2025‑59718.
Exploitability — No public exploit code has been released, but the vulnerability is exploitable remotely without authentication. Fortinet’s advisory assigns a CVSS v3.1 base score of 8.8 (High).
Affected Products — FortiOS (various versions), FortiSwitchMaster, FortiProxy, FortiWeb.
Why It Matters for Trust & Control Assurance
- Demonstrates the need for continuous verification that authentication mechanisms (SAML, SSO) are correctly implemented and monitored.
- Highlights the importance of timely patch management as evidence of due‑diligence in a vendor‑risk program.
- A successful bypass would undermine the integrity of access‑control logs, eroding audit‑ready evidence for regulators and auditors.
Recommended Actions
- Apply the Fortinet security patches referenced in the advisory immediately.
- Validate SAML configuration and signature verification on all Fortinet appliances.
- Update your identity‑and‑access‑management (IAM) policies to require multi‑factor authentication for any SSO path.
- Capture remediation evidence (patch version, configuration snapshots) for audit purposes.
Source: CISA KEV – CVE‑2025‑59718