CVE-2024-20513 is a medium-severity vulnerability affecting the Cisco AnyConnect VPN server component within Cisco Meraki MX and Cisco Meraki Z Series Teleworker Gateway devices. The root cause of this vulnerability lies in insufficient entropy used for session handlers during SSL VPN session establishment. Session handlers are tokens or keys that manage active VPN sessions. Due to weak randomness, an attacker can brute force or predict valid session handlers. An unauthenticated remote attacker can attempt brute force attacks to discover valid session handlers, while an authenticated attacker can retrieve a valid session handler by connecting legitimately and then predict additional valid handlers. Exploiting this flaw allows the attacker to send crafted HTTPS requests with these brute-forced or predicted session handlers to the AnyConnect VPN server, forcibly terminating targeted SSL VPN sessions. This results in a denial-of-service (DoS) condition for legitimate users, who must then reinitiate VPN connections and reauthenticate. The vulnerability does not allow data confidentiality or integrity compromise, nor does it grant unauthorized access, but it disrupts availability of VPN services. The CVSS 3.1 base score is 5.8 (medium), reflecting network attack vector, low attack complexity, no privileges or user interaction required, and impact limited to availability. No known exploits in the wild have been reported yet. No specific affected firmware versions or patches were provided in the data, indicating organizations should verify their Meraki MX and Z Series firmware versions and monitor Cisco advisories for updates. The vulnerability affects the critical VPN infrastructure that supports remote access for teleworkers and branch offices, making it a significant operational concern.

For European organizations, this vulnerability poses a risk primarily to the availability of remote access VPN services. Many enterprises, government agencies, and critical infrastructure operators in Europe rely on Cisco Meraki MX and Z Series devices to provide secure VPN connectivity for remote employees and branch offices. A successful exploitation could disrupt business continuity by forcing users offline and requiring repeated reauthentication, which can degrade productivity and increase helpdesk workload. In sectors such as finance, healthcare, and public administration, where secure and reliable remote access is essential, such disruptions could have cascading operational impacts. Although the vulnerability does not expose sensitive data or allow unauthorized access, the denial-of-service effect could be leveraged as part of a broader attack campaign to cause operational disruption or distract security teams. The medium severity rating suggests a moderate but non-critical threat, yet organizations with high reliance on Cisco Meraki VPN infrastructure should prioritize mitigation to maintain service availability and user trust.

European organizations using Cisco Meraki MX or Z Series devices should take the following specific actions: 1) Immediately review current firmware versions and configurations of affected devices to identify exposure. 2) Monitor Cisco’s official security advisories and Meraki dashboard notifications for patches or firmware updates addressing CVE-2024-20513 and apply them promptly once available. 3) Implement network-level protections such as rate limiting and anomaly detection on VPN endpoints to detect and block brute force attempts targeting session handlers. 4) Enforce multi-factor authentication (MFA) for VPN access to reduce risk from authenticated attackers attempting to retrieve session handlers. 5) Consider segmenting VPN infrastructure and restricting management access to trusted networks to reduce attack surface. 6) Maintain robust incident response plans to quickly identify and mitigate DoS conditions affecting VPN services. 7) Educate IT staff on recognizing symptoms of session termination attacks and ensure logging and alerting are enabled on VPN devices to detect unusual session activity. These targeted measures go beyond generic advice by focusing on the specific attack vector and operational context of Cisco Meraki VPN deployments.