CVE-2024-39874 is a high-severity vulnerability affecting Siemens SINEMA Remote Connect Server versions prior to 3.2 SP1. The vulnerability stems from improper restriction of excessive authentication attempts (CWE-307) in the Client Communication component of the application. Specifically, the affected versions do not implement adequate brute force protection mechanisms, such as account lockout, rate limiting, or CAPTCHA challenges, allowing an attacker to repeatedly attempt to guess user credentials without being blocked or slowed down. This flaw enables an unauthenticated remote attacker to perform brute force attacks against user accounts over the network, potentially discovering valid credentials. The CVSS 3.1 base score is 7.5, reflecting the network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), high confidentiality impact (C:H), but no impact on integrity or availability (I:N/A:N). The vulnerability is publicly disclosed as of July 9, 2024, but no known exploits in the wild have been reported yet. Siemens has not yet published patches or mitigations at the time of this report. The vulnerability is critical for environments where SINEMA Remote Connect Server is used to manage remote connections to industrial control systems (ICS) or critical infrastructure, as compromised credentials could allow unauthorized access to sensitive network segments or control systems.

For European organizations, especially those in critical infrastructure sectors such as energy, manufacturing, transportation, and utilities, this vulnerability poses a significant risk. SINEMA Remote Connect Server is widely used in industrial environments to securely manage remote access to control systems. Successful exploitation could lead to unauthorized access to operational technology (OT) networks, potentially enabling espionage, sabotage, or disruption of industrial processes. The confidentiality impact is high because attackers can gain legitimate credentials, bypassing other security controls. Although integrity and availability are not directly impacted by the vulnerability itself, the subsequent misuse of compromised credentials could lead to further attacks affecting system integrity or availability. The lack of brute force protection also increases the risk of credential compromise in environments where password policies may be weak or reused. European organizations with extensive Siemens ICS deployments are particularly at risk, and the threat is amplified by the increasing targeting of European critical infrastructure by advanced persistent threat (APT) groups.

1. Immediate deployment of the latest Siemens SINEMA Remote Connect Server version 3.2 SP1 or later once available, as this version addresses the vulnerability. 2. Until patches are available, implement network-level protections such as restricting access to the SINEMA Remote Connect Server management interfaces to trusted IP addresses or VPNs. 3. Enable multi-factor authentication (MFA) for all user accounts accessing the SINEMA Remote Connect Server to mitigate the risk of credential compromise via brute force. 4. Monitor authentication logs for repeated failed login attempts and implement alerting to detect brute force activity early. 5. Enforce strong password policies and encourage regular password changes to reduce the risk of credential guessing. 6. Consider deploying web application firewalls (WAFs) or intrusion prevention systems (IPS) with rate-limiting or brute force detection capabilities in front of the SINEMA Remote Connect Server. 7. Conduct regular security audits and penetration tests focusing on authentication mechanisms in ICS remote access solutions. 8. Educate operational staff about the risks of credential compromise and the importance of secure remote access practices.