CVE-2024-20502 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 is insufficient resource management during the establishment of SSL VPN sessions. Specifically, an unauthenticated, remote attacker can exploit this flaw by sending a series of specially crafted HTTPS requests to the VPN server. This triggers uncontrolled resource consumption, leading to a denial-of-service (DoS) condition where the VPN server stops accepting new SSL VPN connections. Importantly, existing SSL VPN sessions remain unaffected, and the server recovers gracefully once the attack traffic ceases, without requiring manual intervention. The vulnerability has a CVSS v3.1 base score of 5.8, reflecting its medium severity, with an attack vector of network (remote), low attack complexity, no privileges required, no user interaction, and a scope change. No known exploits are currently reported in the wild, and no specific affected firmware versions or patches have been detailed in the provided information. The vulnerability impacts the availability of the VPN service, potentially disrupting remote access capabilities for organizations relying on Cisco Meraki MX and Z Series devices for secure connectivity.

For European organizations, this vulnerability poses a risk to the availability of critical VPN infrastructure that supports remote work and secure access to corporate networks. Disruption of SSL VPN connectivity can hinder employee productivity, delay business operations, and impact incident response capabilities, especially in sectors with high reliance on remote access such as finance, healthcare, and government. While confidentiality and integrity are not directly impacted, the denial of new VPN connections can prevent legitimate users from establishing secure sessions, potentially forcing fallback to less secure or alternative access methods. Organizations with large deployments of Cisco Meraki MX or Z Series devices, particularly those supporting teleworker or hybrid work models, may experience operational disruptions during exploitation attempts. The graceful recovery feature reduces the risk of prolonged outages but does not eliminate the temporary denial of service impact. Additionally, given the increasing geopolitical tensions and cyber threat activity targeting European critical infrastructure, attackers may leverage this vulnerability as part of broader disruptive campaigns.

To mitigate this vulnerability, European organizations should prioritize the following actions: 1) Monitor Cisco security advisories closely for official patches or firmware updates addressing CVE-2024-20502 and apply them promptly once available. 2) Implement network-level protections such as rate limiting and anomaly detection on HTTPS traffic directed at the VPN server to identify and block suspicious patterns indicative of resource exhaustion attacks. 3) Employ intrusion prevention systems (IPS) or next-generation firewalls capable of detecting and mitigating DoS attempts targeting VPN infrastructure. 4) Segment VPN servers from general network traffic where possible to reduce exposure and limit attack surface. 5) Maintain robust logging and alerting on VPN server connection attempts to enable rapid detection of exploitation attempts. 6) Develop and test incident response plans that include procedures for handling VPN service disruptions to minimize operational impact. 7) Consider deploying redundant VPN gateways or load-balanced configurations to improve resilience against DoS conditions. These measures go beyond generic advice by focusing on proactive detection, network-level controls, and operational preparedness specific to the nature of this vulnerability.