CVE-2026-25815 identifies a cryptographic weakness in Fortinet FortiOS versions through 7.6.6, where LDAP credentials stored in device configuration files are encrypted using a default cryptographic key that is identical across all customer installations. This default key usage falls under CWE-1394 (Use of Default Cryptographic Key), which undermines the confidentiality of stored credentials. Attackers with local access to the device configuration files can decrypt these LDAP credentials, potentially gaining unauthorized access to LDAP services. The vendor's stance is that this is not a vulnerability if customers enable a non-default encryption option that uses unique keys per installation, but this option is disabled by default because enabling it can disrupt FortiGate management functionality, as documented in Fortinet's "Managing FortiGates with private data encryption" guide. The vulnerability has a CVSS 3.1 base score of 3.2, reflecting low severity due to the requirement for local access, high attack complexity, no privileges required, and no user interaction. The scope is considered changed because the confidentiality of LDAP credentials is impacted, but integrity and availability remain unaffected. Although exploitation in the wild has been reported since December 2025, no public exploit code or widespread attacks have been documented. The vulnerability primarily threatens organizations that have not enabled the stronger encryption option and rely on FortiOS devices for LDAP authentication, as attackers could leverage decrypted credentials to access directory services and potentially escalate privileges or move laterally within networks.

For European organizations, the exposure of LDAP credentials due to this vulnerability can lead to unauthorized access to directory services, which are critical for authentication and authorization in enterprise environments. This could facilitate lateral movement, privilege escalation, and data exfiltration if attackers gain footholds within networks. Although the vulnerability requires local access to device configuration files, insider threats or attackers who have already compromised network segments could exploit it. The impact is particularly significant for sectors relying heavily on Fortinet FortiOS devices for network security and LDAP-based authentication, such as government agencies, financial institutions, healthcare providers, and critical infrastructure operators. The confidentiality breach of LDAP credentials could undermine trust in identity management systems and complicate incident response efforts. However, the lack of impact on integrity and availability, combined with the high attack complexity and local access requirement, limits the overall risk. Still, organizations that do not enable the recommended encryption option remain vulnerable to credential compromise, which could cascade into broader security incidents.

European organizations should immediately audit their FortiOS devices to determine if the default cryptographic key setting is in use for LDAP credential encryption. They should enable the non-default encryption option that uses unique cryptographic keys per installation, despite potential disruptions, and plan for operational adjustments accordingly. To minimize disruption, testing this configuration in controlled environments before widespread deployment is advised. Additionally, organizations should restrict local access to FortiOS device configuration files through strict access controls, monitoring, and logging to detect unauthorized access attempts. Employing network segmentation and limiting administrative privileges can reduce the risk of attackers obtaining local access. Regularly updating FortiOS to the latest versions, once patches or improved configurations are available, is critical. Organizations should also consider implementing multi-factor authentication for LDAP services and monitoring for anomalous authentication activities that might indicate credential misuse. Finally, educating administrators about the risks of default cryptographic keys and the importance of secure configuration management will help prevent similar issues.