CVE-2024-20498 is a high-severity vulnerability affecting the Cisco AnyConnect VPN server component within Cisco Meraki MX and Cisco Meraki Z Series Teleworker Gateway devices. The vulnerability arises from a double free condition caused by insufficient validation of client-supplied parameters during the establishment of SSL VPN sessions. An unauthenticated remote attacker can exploit this flaw by sending specially crafted HTTPS requests to the VPN server. Successful exploitation results in a denial-of-service (DoS) condition where the AnyConnect VPN server process restarts, disrupting all active SSL VPN connections. This forces remote users to reauthenticate and reestablish their VPN sessions. If the attacker sustains the attack, they can prevent new SSL VPN connections from being established, effectively blocking remote access through the VPN. Importantly, the vulnerability does not lead to confidentiality or integrity compromise but impacts availability. The Cisco AnyConnect VPN server recovers automatically once the attack traffic ceases, requiring no manual intervention. The CVSS v3.1 base score is 8.6, reflecting the ease of exploitation (network vector, no privileges or user interaction required) and the significant impact on availability with a scope change, as the vulnerability affects the VPN service that supports multiple users. No known exploits in the wild have been reported yet, and no specific affected firmware versions or patches were provided in the data. This vulnerability is critical for organizations relying on Cisco Meraki MX or Z Series devices for secure remote access, as it can disrupt business continuity by denying VPN access to remote employees or partners.

For European organizations, this vulnerability poses a significant risk to business continuity and remote workforce productivity. Many enterprises and public sector entities in Europe use Cisco Meraki MX and Z Series devices to provide secure VPN access for remote employees, especially in the context of hybrid work models. A successful DoS attack could interrupt access to corporate networks, critical applications, and data, delaying operations and potentially causing financial and reputational damage. Sectors such as finance, healthcare, government, and critical infrastructure, which heavily depend on secure and reliable VPN connectivity, are particularly vulnerable. Additionally, the disruption of VPN services could hinder compliance with data protection regulations like GDPR if it impacts timely access to data or incident response capabilities. While the vulnerability does not allow data theft or manipulation, the availability impact alone can have cascading effects on operational resilience and incident management.

Organizations should immediately assess their deployment of Cisco Meraki MX and Z Series Teleworker Gateway devices to determine exposure. Specific mitigation steps include: 1) Monitoring Cisco’s official advisories for firmware updates or patches addressing CVE-2024-20498 and applying them promptly once available. 2) Implementing network-level protections such as rate limiting and filtering to restrict or block suspicious HTTPS requests targeting the VPN server, thereby reducing the risk of exploitation. 3) Employing intrusion detection and prevention systems (IDS/IPS) tuned to detect anomalous SSL VPN session establishment patterns indicative of exploitation attempts. 4) Enhancing VPN server logging and monitoring to quickly identify and respond to service restarts or unusual connection failures. 5) Considering temporary alternative remote access solutions or failover mechanisms to maintain business continuity during patch deployment. 6) Educating IT staff on the vulnerability’s characteristics to improve incident response readiness. Given the automatic recovery behavior, ensuring rapid detection and mitigation of sustained attacks is critical to minimize downtime.