CVE-2025-58903 is a vulnerability identified in Fortinet's FortiOS, specifically affecting versions 7.6.0 through 7.6.3 and earlier versions before 7.4.8. The flaw stems from an unchecked return value in the FortiOS API, categorized under CWE-252, which leads to a null pointer dereference when processing a specially crafted request. This causes the HTTP daemon responsible for handling API requests to crash, resulting in a denial of service (DoS) condition. The vulnerability requires the attacker to be authenticated to the system, indicating that external unauthenticated attackers cannot exploit it directly. No user interaction is necessary once authenticated, and the attack can be executed remotely over the network. The CVSS v3.1 base score is 2.5, reflecting low severity primarily due to the requirement for high privileges (authenticated user) and the limited impact confined to availability without affecting confidentiality or integrity. There are no known exploits in the wild at this time, and no official patches have been linked yet, though Fortinet is expected to release updates addressing this issue. The vulnerability affects multiple major FortiOS versions, including 6.4.0, 7.0.0, 7.2.0, 7.4.0, and 7.6.0, indicating a broad potential impact across deployments using these versions.

For European organizations, the primary impact of CVE-2025-58903 is the potential disruption of network security services provided by FortiOS devices. Since FortiOS is widely used in enterprise firewalls, VPN gateways, and other security appliances, a successful exploit could cause temporary denial of service, leading to loss of network connectivity or degraded security monitoring. This could affect business continuity, especially for critical infrastructure sectors such as finance, healthcare, energy, and government services that rely heavily on Fortinet products for perimeter defense and secure remote access. However, since exploitation requires authenticated access, the risk of external attackers causing widespread outages is reduced. Insider threats or compromised credentials could be leveraged to exploit this vulnerability. The absence of confidentiality or integrity impact means data breaches or manipulation are unlikely from this flaw alone. Nonetheless, availability interruptions could indirectly affect compliance with European regulations like GDPR if service outages impact data processing or availability commitments.

Organizations should prioritize applying official Fortinet patches as soon as they become available to remediate this vulnerability. Until patches are released, administrators should restrict API access to trusted and minimal sets of authenticated users, employing strong authentication mechanisms such as multi-factor authentication (MFA). Network segmentation should be enforced to limit access to FortiOS management interfaces, ideally isolating them from general user networks. Monitoring and logging of API access attempts should be enhanced to detect unusual or suspicious activity that could indicate exploitation attempts. Regularly reviewing and rotating credentials for FortiOS administrative accounts will reduce the risk of credential compromise. Additionally, organizations can implement rate limiting or other network controls to mitigate potential denial of service attempts targeting the HTTP daemon. Incident response plans should include procedures for rapid recovery from FortiOS service crashes to minimize downtime.