CVE-2025-24471 is a vulnerability identified in Fortinet's FortiOS, specifically affecting versions 7.6.1 and below, as well as 7.4.7 and below. The issue stems from improper certificate validation (classified under CWE-295), where the system fails to correctly verify the revocation status of certificates used during the Extensible Authentication Protocol (EAP) process. This flaw allows a remote user, authenticated via EAP and connecting through FortiClient, to establish a connection even when using a revoked certificate. Essentially, the FortiOS device does not enforce proper access control by accepting credentials that should have been invalidated, undermining the integrity of the authentication mechanism. The vulnerability has a CVSS 3.1 base score of 6.0, indicating a medium severity level. The vector details highlight that the attack can be performed remotely over the network (AV:N) with low attack complexity (AC:L), requiring privileges (PR:L) but no user interaction (UI:N). The impact is primarily on integrity (I:H), with no direct confidentiality or availability impact. Exploitation could allow an attacker with some level of access to bypass certificate revocation checks, potentially gaining unauthorized network access or escalating privileges within the Fortinet environment. No known exploits are currently reported in the wild, and no patches or mitigation links are provided in the source data, indicating that organizations should proactively monitor Fortinet advisories for updates. This vulnerability is critical in environments relying on FortiOS for secure VPN or network access control, where certificate-based authentication is a key security control.

For European organizations, the improper certificate validation vulnerability in FortiOS poses a significant risk to network security, especially for enterprises and government agencies that depend on Fortinet's VPN and network security appliances for remote access. The ability for an attacker to connect using a revoked certificate undermines trust in the authentication process, potentially allowing unauthorized access to sensitive internal resources. This could lead to lateral movement within networks, data integrity breaches, and unauthorized configuration changes. Given the widespread use of Fortinet products in Europe across sectors such as finance, healthcare, telecommunications, and critical infrastructure, exploitation could disrupt business operations and compromise sensitive data. The medium severity rating suggests that while exploitation requires some privileges, the lack of user interaction and remote attack vector makes it a feasible threat. European organizations with remote workforce setups or those employing FortiClient for VPN access are particularly vulnerable. Additionally, regulatory frameworks like GDPR emphasize the protection of personal data, and unauthorized access resulting from this vulnerability could lead to compliance violations and financial penalties.

To mitigate this vulnerability, European organizations should: 1) Immediately review and update FortiOS devices to the latest firmware versions once Fortinet releases patches addressing CVE-2025-24471. 2) Implement strict certificate lifecycle management, including timely revocation and monitoring of certificate status to detect anomalies. 3) Enforce multi-factor authentication (MFA) alongside certificate-based authentication to add an additional security layer, reducing reliance solely on certificates. 4) Conduct regular audits of VPN and remote access logs to identify suspicious connections potentially using revoked certificates. 5) Restrict administrative privileges to minimize the risk of attackers gaining the required privilege level to exploit this vulnerability. 6) Employ network segmentation to limit the impact of any unauthorized access gained through this flaw. 7) Stay informed through Fortinet security advisories and subscribe to threat intelligence feeds to detect emerging exploit attempts. These steps go beyond generic advice by focusing on certificate management, layered authentication, and proactive monitoring tailored to the nature of this vulnerability.