CVE-2026-25815 identifies a cryptographic weakness in Fortinet FortiOS versions through 7.6.6, where LDAP credentials stored within device configuration files are encrypted using a default cryptographic key that is identical across all customer installations. This design flaw corresponds to CWE-1394, 'Use of Default Cryptographic Key,' which undermines the confidentiality of sensitive credentials. Attackers with local access to the device configuration files can decrypt these LDAP credentials without needing authentication or user interaction. The vulnerability arises because Fortinet’s default configuration does not enable a stronger encryption option that uses unique keys per installation; this option is disabled by default due to potential disruptions in device management functionality, as documented in Fortinet’s 'Managing FortiGates with private data encryption' guide. The CVSS v3.1 base score is 3.2 (low severity), reflecting a local attack vector, high attack complexity, no privileges required, no user interaction, and limited confidentiality impact. No known exploits have been observed in the wild as of the publication date. The vulnerability affects all FortiOS devices up to version 7.6.6 that have not enabled the recommended encryption setting. This weakness could allow attackers who gain access to configuration files—through other means such as compromised administrative credentials or physical access—to extract LDAP credentials, potentially facilitating further lateral movement or privilege escalation within enterprise 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 across enterprise environments. Compromise of LDAP credentials may enable attackers to impersonate users, escalate privileges, or access sensitive resources, undermining confidentiality and potentially integrity of systems. Although the vulnerability requires local access to configuration files, attackers who have already breached perimeter defenses or insider threats could exploit this to deepen their foothold. The low CVSS score reflects limited direct impact and high exploitation complexity, but the cascading effects of credential compromise in complex enterprise networks can be significant. Organizations relying heavily on Fortinet FortiOS for network security and authentication infrastructure, especially those in regulated sectors such as finance, healthcare, and critical infrastructure within Europe, face increased risk. The default use of a shared cryptographic key across all installations amplifies the risk since compromise of one device’s configuration could reveal credentials applicable to others if reused. However, the lack of known active exploitation reduces immediate threat urgency.

European organizations should prioritize enabling the non-default private data encryption option in FortiOS that uses unique cryptographic keys per installation, despite potential operational disruptions. This setting is documented by Fortinet and is the definitive fix to eliminate the use of default cryptographic keys. Before enabling, thorough testing in controlled environments is recommended to assess and mitigate any functional impacts on device management workflows. Additionally, organizations should enforce strict access controls to FortiOS configuration files, limiting access to trusted administrators and using secure storage and transmission methods. Regular audits and monitoring for unauthorized access to configuration files can help detect potential exploitation attempts. Network segmentation and strong endpoint security can reduce the risk of attackers gaining local access to devices. Organizations should also keep FortiOS firmware updated and monitor Fortinet advisories for patches or improvements addressing this issue. Finally, consider integrating multi-factor authentication and enhanced logging around LDAP and FortiOS administrative access to detect anomalous activities early.