CVE-2025-59718: Fortinet Multiple Products Improper Verification of Cryptographic Signature Vulnerability

In short

Fortinet Multiple Products has a weakness classified as improper verification of cryptographic signature (CWE-347). CISA added it to its Known Exploited Vulnerabilities catalog on 2025-12-16. NVD lists CVSS 3.1 at 9.8 CRITICAL.

What it is

“Fortinet FortiOS, FortiSwitchMaster, FortiProxy, and FortiWeb contain an improper verification of cryptographic signature vulnerability that may allow an unauthenticated attacker to bypass the FortiCloud SSO login authentication via a crafted SAML message. Please be aware that CVE-2025-59719 pertains to the same problem and is mentioned in the same vendor advisory. Ensure to apply all patches mentioned in the advisory.” — CISA KEV, retrieved 2026-11-01

“A improper verification of cryptographic signature vulnerability in Fortinet FortiOS 7.6.0 through 7.6.3, FortiOS 7.4.0 through 7.4.8, FortiOS 7.2.0 through 7.2.11, FortiOS 7.0.0 through 7.0.17, FortiProxy 7.6.0 through 7.6.3, FortiProxy 7.4.0 through 7.4.10, FortiProxy 7.2.0 through 7.2.14, FortiProxy 7.0.0 through 7.0.21, FortiSwitchManager 7.2.0 through 7.2.6, FortiSwitchManager 7.0.0 through 7.0.5 allows an unauthenticated attacker to bypass the FortiCloud SSO login authentication via a crafted SAML response message.” — NVD, retrieved 2026-11-01

Who is affected

Fortinet Multiple Products. NVD lists the following versions as affected:

• Fortinet Fortiproxy: from 7.0.0 inclusive, before 7.0.22
• Fortinet Fortiproxy: from 7.2.0 inclusive, before 7.2.15
• Fortinet Fortiproxy: from 7.4.0 inclusive, before 7.4.11
• Fortinet Fortiproxy: from 7.6.0 inclusive, before 7.6.4
• Fortinet Fortiswitchmanager: from 7.0.0 inclusive, before 7.0.6
• Fortinet Fortiswitchmanager: from 7.2.0 inclusive, before 7.2.7
• Fortinet Fortios: from 7.0.0 inclusive, before 7.0.18
• Fortinet Fortios: from 7.2.0 inclusive, before 7.2.12
• Fortinet Fortios: from 7.4.0 inclusive, before 7.4.9
• Fortinet Fortios: from 7.6.0 inclusive, before 7.6.4
• Siemens Ruggedcom ape1808 Firmware: all versions listed (no range given)

Exploitation status

CISA KEV added: 2025-12-16. Known ransomware campaign use: Not reported by CISA. Due date CISA set for US federal civilian agencies: 2025-12-23.

Scores

NVD CVSS 3.1: 9.8 CRITICAL; vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H; source [email protected].

EPSS by FIRST: 68.29%; percentile 99.33; score date 2026-10-31. EPSS estimates the probability of exploitation in the next 30 days.

CWE: CWE-347.

Timeline

CISA required action

“Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.” — CISA KEV

What to do

• Confirm whether you run Fortinet Multiple Products and which version.
• Apply the vendor update or mitigation in the advisory.
• Follow CISA’s required action.
• Review the vendor guidance on signs of compromise.
• Track the fix through completion.

References

• Vendor Advisory: https://fortiguard.fortinet.com/psirt/FG-IR-25-647
• Third Party Advisory: https://arcticwolf.com/resources/blog/arctic-wolf-observes-malicious-sso-logins-following-disclosure-cve-2025-59718-cve-2025-59719/
• Third Party Advisory: https://cert-portal.siemens.com/productcert/html/ssa-864900.html
• NVD detail
• CVE.org record
• CISA KEV catalog

Sources and dates

CISA Known Exploited Vulnerabilities Catalog, version 2026.10.30; retrieved 2026-11-01. CISA KEV data: CC0 1.0. No endorsement by CISA.

NVD retrieved: 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.

EPSS scores by FIRST; score date 2026-10-31.