CVE-2024-20499 in Meraki MX
Summary
by MITRE • 10/02/2024
Multiple vulnerabilities in the Cisco AnyConnect VPN server of Cisco Meraki MX and Cisco Meraki Z Series Teleworker Gateway devices could allow an unauthenticated, remote attacker to cause a DoS condition in the AnyConnect service on an affected device.
These vulnerabilities are due to insufficient validation of client-supplied parameters while establishing an SSL VPN session. An attacker could exploit these vulnerabilities by sending a crafted HTTPS request to the VPN server of an affected device. A successful exploit could allow the attacker to cause the Cisco AnyConnect VPN server to restart, resulting in the failure of the established SSL VPN connections and forcing remote users to initiate a new VPN connection and reauthenticate. A sustained attack could prevent new SSL VPN connections from being established. Note: When the attack traffic stops, the Cisco AnyConnect VPN server recovers gracefully without requiring manual intervention.
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Analysis
by VulDB Data Team • 07/03/2025
The vulnerability identified as CVE-2024-20499 represents a critical security flaw affecting Cisco Meraki MX and Z Series Teleworker Gateway devices that implement Cisco AnyConnect VPN services. This issue stems from inadequate input validation mechanisms within the SSL VPN session establishment process, creating an exploitable condition that allows unauthenticated remote attackers to disrupt service availability. The vulnerability specifically targets the AnyConnect VPN server component, which serves as the primary interface for remote network access through SSL VPN connections. These devices operate in environments where secure remote access is essential for business continuity, making the potential impact of this vulnerability particularly severe for organizations relying on Meraki gateway solutions.
The technical exploitation of this vulnerability occurs through the manipulation of client-supplied parameters during SSL VPN session initiation, specifically targeting the HTTPS request handling mechanism. Attackers can craft malicious requests that bypass proper validation checks, causing the AnyConnect VPN server to experience unexpected behavior leading to service disruption. This flaw operates at the protocol level where the server fails to adequately sanitize or validate incoming parameters, allowing malformed input to trigger system instability. The vulnerability manifests as a denial-of-service condition that forces the VPN server to restart automatically, effectively terminating existing connections and preventing new ones from being established. The root cause aligns with CWE-20, which describes improper input validation as a fundamental weakness in software security design that allows malicious inputs to disrupt normal application behavior.
The operational impact of CVE-2024-20499 extends beyond simple service interruption to create significant business continuity concerns for organizations utilizing Meraki gateway solutions. When exploited, the vulnerability creates a cascading effect where remote users experience forced disconnections requiring reauthentication, potentially disrupting critical business operations and productivity. The sustained nature of attacks can prevent new VPN connections from being established, effectively blocking remote access entirely and compromising the organization's ability to maintain secure remote workforce access. Organizations relying on these devices for teleworker connectivity face potential operational downtime that could impact customer service, remote work capabilities, and overall business resilience. The automatic recovery mechanism provides some relief, but the repeated disruption of service creates operational friction and potential security concerns during the recovery periods.
Mitigation strategies for this vulnerability should prioritize immediate patch deployment as provided by Cisco, which addresses the underlying input validation deficiencies in the AnyConnect VPN server implementation. Network administrators should implement monitoring solutions to detect anomalous traffic patterns that may indicate exploitation attempts, particularly focusing on unusual HTTPS request sequences targeting the VPN server endpoints. Access controls should be enhanced to limit exposure of VPN services to trusted networks only, while implementing rate limiting mechanisms to prevent rapid exploitation attempts. Organizations should also establish incident response procedures that account for VPN service disruptions, including backup communication channels and alternative remote access methods. The vulnerability demonstrates the importance of proper input validation in security-critical components and aligns with ATT&CK technique T1499.004 for network denial of service attacks, emphasizing the need for robust server-side validation mechanisms to prevent exploitation through malformed inputs.