CVE-2026-22153 is an authentication bypass vulnerability identified in Fortinet FortiOS versions 7.6.0 through 7.6.4. The flaw arises due to improper access control in the LDAP authentication process for Agentless VPN and Fortinet Single Sign-On (FSSO) policies. Specifically, when the remote LDAP server is configured in a particular way, an unauthenticated attacker can bypass the LDAP authentication mechanism entirely. This vulnerability is categorized under CWE-305 (Authentication Bypass by Primary Weakness). The attacker does not require any prior authentication or user interaction and can exploit this remotely over the network. The CVSS v3.1 base score is 7.5, indicating high severity, with a vector indicating network attack vector (AV:N), high attack complexity (AC:H), no privileges required (PR:N), no user interaction (UI:N), and full impact on confidentiality, integrity, and availability (C:H/I:H/A:H). The vulnerability could allow attackers to gain unauthorized access to VPN or FSSO-protected resources, potentially leading to data exfiltration, lateral movement within networks, or disruption of services. Although no known exploits are currently reported in the wild, the presence of this vulnerability in widely deployed FortiOS versions necessitates immediate attention. The lack of patch links suggests that patches may be forthcoming or that organizations should monitor Fortinet advisories closely. The vulnerability impacts critical security functions, making it a significant risk for organizations relying on Fortinet's VPN and authentication infrastructure.

For European organizations, the impact of CVE-2026-22153 can be severe. Fortinet FortiOS is widely used across Europe in enterprises, government agencies, and critical infrastructure sectors for secure remote access and identity management. Successful exploitation could allow attackers to bypass authentication controls, gaining unauthorized access to internal networks via VPN or FSSO mechanisms. This can lead to exposure of sensitive data, disruption of business operations, and potential compromise of other connected systems through lateral movement. Given the high confidentiality, integrity, and availability impacts, organizations could face regulatory penalties under GDPR if personal data is compromised. Additionally, critical infrastructure sectors such as energy, finance, and healthcare that rely on Fortinet devices for secure access could experience operational disruptions or targeted attacks. The high attack complexity somewhat limits exploitation but does not eliminate risk, especially from skilled threat actors. The absence of known exploits currently provides a window for mitigation, but the risk remains substantial due to the critical nature of the affected components.

1. Monitor Fortinet security advisories closely and apply official patches or updates for FortiOS versions 7.6.0 through 7.6.4 as soon as they become available. 2. Review and harden LDAP server configurations to avoid the specific setups that enable authentication bypass; consult Fortinet documentation or support for recommended secure LDAP configurations. 3. Implement network segmentation to restrict access to FortiOS management and authentication interfaces, limiting exposure to untrusted networks. 4. Employ multi-factor authentication (MFA) for VPN access where possible to add an additional layer of security beyond LDAP authentication. 5. Conduct thorough audits of VPN and FSSO policies to detect any anomalous or unauthorized access attempts. 6. Increase monitoring and logging of authentication events on FortiOS devices to detect potential exploitation attempts early. 7. Consider temporary mitigations such as disabling Agentless VPN or FSSO features if they are not critical or if secure LDAP configurations cannot be guaranteed. 8. Educate security teams on the specifics of this vulnerability to ensure rapid response and incident handling if exploitation is suspected.