CVE-2023-41840 is a vulnerability in Fortinet's FortiClientWindows software, specifically versions 7.0.9 and 7.2.0, that allows escalation of privilege through a DLL hijacking attack. The root cause is an untrusted search path vulnerability where the application loads OpenSSL engine libraries from directories that can be influenced by an attacker. By placing a malicious DLL mimicking the OpenSSL engine library in a directory earlier in the search path, an attacker with low-level local access can trick FortiClientWindows into loading this malicious code. This results in execution of arbitrary code with elevated privileges, potentially allowing the attacker to gain administrative rights on the system. The vulnerability does not require user interaction but does require local access with some privileges (low). The CVSS v3.1 score of 7.4 (high) reflects the attack vector as local (AV:L), low attack complexity (AC:L), privileges required (PR:L), no user interaction (UI:N), and high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). Although no exploits have been reported in the wild yet, the vulnerability poses a significant risk due to the widespread use of FortiClientWindows in enterprise environments for VPN and endpoint security. The absence of patch links suggests that organizations should monitor Fortinet advisories closely for updates. The vulnerability highlights the importance of secure DLL loading practices and restricting write permissions on directories in the search path.

For European organizations, the impact of CVE-2023-41840 can be severe. FortiClientWindows is commonly deployed in enterprises and government agencies for secure remote access and endpoint protection. Exploitation could allow attackers who have gained low-level access (e.g., via phishing or insider threats) to escalate privileges to administrative levels, leading to full system compromise. This could result in data breaches, disruption of critical services, and lateral movement within networks. Sectors such as finance, healthcare, energy, and government are particularly at risk due to their reliance on Fortinet products and the sensitive nature of their data and operations. The vulnerability could also undermine trust in VPN connections, potentially exposing confidential communications. Given the high impact on confidentiality, integrity, and availability, the threat could facilitate espionage, ransomware deployment, or sabotage. The lack of known exploits in the wild currently reduces immediate risk but does not diminish the urgency for mitigation.

European organizations should take the following specific steps to mitigate CVE-2023-41840: 1) Immediately audit all systems running FortiClientWindows versions 7.0.9 and 7.2.0 and plan for rapid deployment of patches once available from Fortinet. 2) Until patches are released, restrict write permissions on directories included in the DLL search path to prevent unauthorized DLL placement. 3) Employ application whitelisting and code integrity policies to block loading of untrusted DLLs. 4) Monitor local file system changes and suspicious DLL loads using endpoint detection and response (EDR) tools. 5) Limit local user privileges to the minimum necessary to reduce the risk of privilege escalation. 6) Educate users about the risks of local compromise and enforce strong access controls. 7) Review and harden OpenSSL engine library loading configurations if configurable. 8) Maintain up-to-date asset inventories to quickly identify affected endpoints. 9) Collaborate with Fortinet support channels for timely vulnerability information and remediation guidance. 10) Consider network segmentation to contain potential lateral movement from compromised endpoints.