CVE-2023-20241 is a medium-severity vulnerability affecting Cisco Secure Client software (formerly AnyConnect Secure Mobility Client). The flaw arises from an out-of-bounds memory read condition within the client software. Specifically, an authenticated local attacker on a multi-user system can exploit this vulnerability by logging into the device concurrently with another user who is running Cisco Secure Client. The attacker then sends specially crafted packets to a port on the local host, triggering the out-of-bounds read. This results in a denial of service (DoS) condition by crashing the VPN Agent service, rendering it unavailable to all users on the system. The vulnerability affects numerous versions of Cisco Secure Client, spanning from 4.9.x through 5.0.x releases. Exploitation requires valid user credentials and local access, but no user interaction beyond that is needed. The CVSS v3.1 base score is 5.5 (medium), reflecting that the impact is limited to availability (no confidentiality or integrity impact), requires low privileges (local authenticated user), and has low attack complexity. No known exploits are reported in the wild as of the publication date (November 22, 2023). This vulnerability could disrupt VPN connectivity for users sharing the same system, impacting business continuity and remote access capabilities.

For European organizations, this vulnerability poses a risk primarily to environments where Cisco Secure Client is deployed on multi-user systems, such as shared workstations or terminal servers. The denial of service caused by crashing the VPN Agent service can interrupt secure remote access, potentially halting critical business operations, especially for organizations relying heavily on VPNs for remote workforce connectivity. While the vulnerability does not expose sensitive data or allow privilege escalation, the loss of VPN service availability can degrade productivity and delay incident response activities. Organizations in sectors with high dependency on secure remote access, such as finance, healthcare, government, and critical infrastructure, could experience operational disruptions. Additionally, the requirement for local authenticated access limits the threat to insider attackers or compromised user accounts, which remains a relevant concern for insider threat mitigation in European enterprises.

To mitigate this vulnerability effectively, European organizations should: 1) Identify and inventory all systems running affected versions of Cisco Secure Client, focusing on multi-user environments. 2) Apply Cisco's security patches or updates as soon as they become available, as no patch links are currently provided, monitoring Cisco advisories closely. 3) Restrict local user access on multi-user systems to trusted personnel only, minimizing the risk of malicious or accidental exploitation. 4) Implement strict user account management and monitoring to detect unauthorized or suspicious logins, especially concurrent sessions on the same host. 5) Consider isolating VPN client usage to single-user systems or virtualized environments to reduce multi-user attack surface. 6) Employ endpoint detection and response (EDR) tools to monitor for abnormal process crashes or network activity related to the VPN Agent service. 7) Educate users about the importance of credential security to prevent unauthorized local access. These targeted steps go beyond generic advice by focusing on the unique multi-user aspect and local authentication requirement of this vulnerability.