CVE-2024-20500 in Meraki MX
Summary
by MITRE • 10/02/2024
A vulnerability 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.
This vulnerability is due to insufficient resource management when establishing TLS/SSL sessions. An attacker could exploit this vulnerability by sending a series of crafted TLS/SSL messages to the VPN server of an affected device. A successful exploit could allow the attacker to cause the Cisco AnyConnect VPN server to stop accepting new connections, preventing new SSL VPN connections from being established. Existing SSL VPN sessions are not impacted. 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-2024-20500 represents a critical resource management flaw within the Cisco AnyConnect VPN server implementation on Meraki MX and Z Series Teleworker Gateway devices. This weakness manifests as inadequate handling of TLS/SSL session establishment processes, creating an exploitable condition that can be leveraged by unauthenticated remote attackers. The vulnerability specifically targets the session management mechanisms that govern how the VPN server processes incoming TLS/SSL connections, fundamentally undermining the service availability of the affected devices. The flaw exists in the protocol handling layer where the system fails to properly regulate resource allocation during the secure connection negotiation phase, creating a potential pathway for denial-of-service attacks that directly impact business continuity and remote access capabilities.
From a technical perspective, the vulnerability stems from insufficient resource management during TLS/SSL session initiation, which is classified as a CWE-400 weakness related to resource management failures in network services. The attack vector involves sending carefully crafted TLS/SSL messages that exploit the inadequate session handling mechanisms within the AnyConnect VPN server. These crafted messages trigger resource exhaustion or allocation errors that prevent the server from properly processing new connection requests. The vulnerability operates at the application layer of the network stack, specifically targeting the SSL/TLS handshake process where the server must allocate memory and processing resources to establish secure connections. The implementation lacks proper rate limiting, connection tracking, or resource exhaustion detection mechanisms that would normally prevent such scenarios from causing service disruption.
The operational impact of this vulnerability extends beyond simple service interruption, as it directly affects the availability of critical remote access infrastructure for organizations relying on Cisco Meraki devices for secure connectivity. When exploited successfully, the vulnerability causes the AnyConnect VPN server to cease accepting new connections while maintaining existing sessions, creating a scenario where legitimate users cannot establish new remote access sessions. This disruption can severely impact business operations, particularly for organizations with distributed workforces that depend on secure remote access capabilities. The attack requires minimal privileges and can be executed remotely without authentication, making it particularly dangerous as it can be exploited by threat actors without requiring insider knowledge or credentials. The vulnerability affects the core functionality of the VPN service, potentially creating cascading effects on business operations that rely on remote access for critical functions.
Organizations affected by this vulnerability should implement immediate mitigation strategies focusing on network-level protections and device configuration hardening. The recommended approach includes implementing rate limiting mechanisms at network boundaries to restrict the number of TLS/SSL connection attempts from individual sources, deploying intrusion prevention systems that can detect and block suspicious TLS/SSL traffic patterns, and applying the latest security patches provided by Cisco. Network administrators should also consider implementing monitoring solutions that can detect unusual connection patterns or resource utilization spikes that may indicate exploitation attempts. The vulnerability's recovery characteristics, where the system gracefully recovers without manual intervention once attack traffic ceases, should not be relied upon as a primary defense mechanism, as the repeated exploitation could lead to sustained service degradation. Security teams should establish incident response procedures specifically addressing this vulnerability and consider implementing network segmentation to limit the potential impact of successful exploitation attempts. This vulnerability aligns with ATT&CK technique T1499.004 related to network denial of service attacks and represents a significant concern for organizations operating in environments where remote access availability is critical for operational continuity.