CVE-2026-22153 is an authentication bypass vulnerability identified in Fortinet FortiOS versions 7.6.0 through 7.6.4. The flaw arises from improper access control related to LDAP authentication mechanisms used by Agentless VPN and Fortinet Single Sign-On (FSSO) policies. Specifically, when the remote LDAP server is configured in a particular manner, an unauthenticated attacker can bypass the LDAP authentication process entirely, gaining unauthorized access to the VPN or FSSO-protected resources. This vulnerability is classified under CWE-305 (Authentication Bypass by Primary Weakness), indicating a fundamental flaw in the authentication logic. The CVSS v3.1 base score of 7.5 reflects a high-severity issue with network attack vector, no privileges or user interaction required, but with high attack complexity due to specific LDAP configurations needed for exploitation. The vulnerability affects confidentiality, integrity, and availability, as unauthorized access can lead to data exposure, manipulation, or disruption of services. Although no exploits have been reported in the wild, the presence of this vulnerability in widely deployed FortiOS versions makes it a significant risk. Fortinet has reserved the CVE and published details but has not yet released patches, emphasizing the need for immediate mitigation strategies.

The impact of CVE-2026-22153 is substantial for organizations relying on Fortinet FortiOS 7.6.x for secure remote access and identity management. Successful exploitation allows attackers to bypass LDAP authentication, potentially granting unauthorized access to internal networks, sensitive data, and critical systems. This can lead to data breaches, lateral movement within networks, and disruption of VPN services. The compromise of FSSO policies further exacerbates risks by undermining single sign-on mechanisms, potentially exposing multiple systems to unauthorized access. Organizations in sectors such as finance, healthcare, government, and critical infrastructure are at heightened risk due to the sensitivity of their data and reliance on Fortinet products. The high attack complexity limits widespread exploitation but does not eliminate risk, especially from skilled threat actors targeting specific configurations. The lack of known exploits in the wild currently reduces immediate threat but vigilance is necessary as exploit development may follow disclosure.

1. Immediately review and restrict LDAP server configurations to ensure they do not meet the specific conditions that enable the bypass. 2. Disable Agentless VPN and FSSO policies if not essential until patches are available. 3. Monitor Fortinet advisories closely for official patches and apply them promptly once released. 4. Implement network segmentation to limit access to FortiOS management interfaces and LDAP servers. 5. Employ multi-factor authentication (MFA) on VPN access to add an additional security layer beyond LDAP. 6. Conduct thorough audits of VPN and FSSO logs to detect any anomalous or unauthorized access attempts. 7. Use intrusion detection/prevention systems (IDS/IPS) to monitor for suspicious activity targeting FortiOS devices. 8. Educate IT staff on the vulnerability details and ensure incident response plans include scenarios involving authentication bypass. 9. Consider temporary compensating controls such as IP whitelisting or VPN access restrictions to trusted users only. 10. Regularly update and patch all network infrastructure components to reduce the attack surface.