CVE-2025-40596 is a high-severity stack-based buffer overflow vulnerability identified in the SonicWall SMA 100 Series VPN appliances, specifically affecting versions 10.2.1.15-81sv and earlier. The vulnerability resides in the web interface component of the SMA 100 Series devices. Due to improper bounds checking on input data, an unauthenticated remote attacker can send specially crafted requests that overflow a stack buffer. This overflow can lead to a denial of service (DoS) by crashing the device or, more critically, may allow the attacker to execute arbitrary code with the privileges of the web interface process. The vulnerability is classified under CWE-121, indicating a classic stack-based buffer overflow flaw. The CVSS v3.1 base score is 7.3, reflecting a high severity with network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and impacts on confidentiality, integrity, and availability (C:L/I:L/A:L). No known exploits are currently reported in the wild, and no patches have been linked yet, indicating that organizations using affected versions remain at risk until a fix is released. SonicWall SMA 100 Series devices are commonly deployed as secure remote access VPN gateways in enterprise environments, making this vulnerability a significant threat to network perimeter security.

For European organizations, the impact of this vulnerability could be substantial. SonicWall SMA 100 Series appliances are widely used in enterprise and government sectors for secure remote access, especially in the context of increased remote work. Exploitation could lead to service outages due to DoS, disrupting business continuity and remote workforce connectivity. More severely, successful code execution could allow attackers to gain control over the VPN gateway, potentially leading to unauthorized access to internal networks, data exfiltration, lateral movement, and further compromise of sensitive systems. Confidentiality, integrity, and availability of critical data and services could be jeopardized. Given the unauthenticated nature of the exploit, attackers do not need valid credentials, increasing the risk of opportunistic attacks. The lack of known exploits currently provides a window for mitigation, but the high severity score and ease of exploitation necessitate urgent attention from European organizations relying on these devices.

European organizations should immediately inventory their SonicWall SMA 100 Series devices and verify firmware versions. Until an official patch is released, organizations should consider the following specific mitigations: 1) Restrict access to the SMA 100 Series web interface to trusted management networks only, using network segmentation and firewall rules to block internet-facing access. 2) Implement strict access control lists (ACLs) and VPN gateway hardening to limit exposure. 3) Monitor network traffic for anomalous requests targeting the web interface that could indicate exploitation attempts. 4) Employ intrusion detection/prevention systems (IDS/IPS) with updated signatures to detect potential exploit attempts. 5) Prepare for rapid deployment of patches once available by establishing a vulnerability response plan. 6) Consider temporary alternative remote access solutions if risk exposure is unacceptable. 7) Conduct regular backups of device configurations to enable quick recovery in case of compromise. These targeted steps go beyond generic advice by focusing on reducing attack surface and enhancing detection specific to this vulnerability.