CVE-2025-59719 is a critical security vulnerability affecting Fortinet FortiWeb versions 8.0.0, 7.6.0 through 7.6.4, and 7.4.0 through 7.4.9. The vulnerability arises from improper verification of cryptographic signatures in SAML response messages used in FortiCloud Single Sign-On (SSO) authentication. Specifically, an attacker can craft a malicious SAML response that bypasses the signature verification process, allowing them to impersonate legitimate users without authentication. This bypass effectively grants unauthorized access to the FortiWeb management interface or protected resources, undermining the authentication mechanism. The vulnerability is exploitable remotely over the network without requiring any privileges or user interaction, increasing its risk profile. The CVSS v3.1 score of 9.1 reflects the critical impact on confidentiality, integrity, and availability, as attackers can gain full control over affected systems. FortiWeb is widely deployed as a web application firewall and security gateway, often integrated with FortiCloud services for centralized management and SSO. The flaw compromises the trust model of SAML-based authentication, a widely adopted standard for federated identity management, making this vulnerability particularly dangerous. Although no active exploits have been reported yet, the vulnerability's disclosure and criticality necessitate immediate attention from organizations using FortiWeb appliances.

For European organizations, the impact of CVE-2025-59719 can be severe. Unauthorized access to FortiWeb devices can lead to full compromise of web application firewalls, exposing sensitive internal applications and data to attackers. This can result in data breaches, disruption of critical services, and potential lateral movement within enterprise networks. Organizations relying on FortiWeb for protecting customer-facing applications, internal portals, or compliance-sensitive environments (such as finance, healthcare, and government sectors) face increased risks of regulatory penalties under GDPR due to potential data exposure. The ability to bypass SSO authentication also undermines identity and access management controls, increasing the likelihood of privilege escalation and persistent attacker presence. Given Fortinet's significant market share in Europe, especially among medium to large enterprises and public sector entities, the vulnerability could have widespread consequences if exploited. Additionally, the critical nature of the flaw may attract threat actors aiming to exploit it for espionage, ransomware deployment, or data theft.

European organizations should prioritize the following mitigation steps: 1) Immediately identify and inventory all FortiWeb appliances running affected versions (8.0.0, 7.6.0-7.6.4, 7.4.0-7.4.9). 2) Apply official patches or updates from Fortinet as soon as they become available; if patches are not yet released, engage with Fortinet support for interim fixes or workarounds. 3) Temporarily disable FortiCloud SSO integration or restrict access to the FortiWeb management interface to trusted IP addresses to reduce exposure. 4) Implement network segmentation and strict firewall rules to limit access to FortiWeb devices only to authorized administrators. 5) Monitor logs and network traffic for anomalous SAML responses or authentication bypass attempts. 6) Conduct thorough security assessments and penetration tests focusing on SAML authentication flows. 7) Educate security teams about the vulnerability and update incident response plans to address potential exploitation scenarios. 8) Consider deploying additional multi-factor authentication mechanisms independent of SAML where feasible to add defense-in-depth.