CVE-2025-40600 is a critical vulnerability identified in SonicWall's SonicOS, specifically affecting versions 7.2.0-7015 and earlier. The vulnerability is classified under CWE-134, which pertains to the use of externally-controlled format strings. This type of vulnerability arises when user-supplied input is unsafely incorporated into format string functions, potentially allowing an attacker to manipulate the format string parameters. In this case, the flaw exists in the SonicOS SSL VPN interface, a component that facilitates secure remote access to internal networks. The vulnerability allows a remote attacker, without any authentication or user interaction, to exploit the format string flaw to cause service disruption. The CVSS v3.1 base score of 9.8 reflects the critical severity, indicating high impact on confidentiality, integrity, and availability. The attack vector is network-based (AV:N), requires no privileges (PR:N), and no user interaction (UI:N), making exploitation straightforward. Successful exploitation could lead to denial of service (DoS) conditions, potentially crashing the SSL VPN service or the entire device, thereby disrupting remote access capabilities. Although no known exploits are currently reported in the wild, the ease of exploitation and critical impact necessitate urgent attention. SonicWall devices running vulnerable SonicOS versions are at risk, particularly those exposed to untrusted networks where attackers can reach the SSL VPN interface. The lack of available patches at the time of publication increases the urgency for mitigation through configuration changes or network-level protections.

For European organizations, the impact of this vulnerability could be severe. SonicWall appliances are widely used in enterprise and government sectors across Europe to provide secure remote access. Exploitation could lead to significant service outages, disrupting business continuity, remote workforce operations, and access to critical internal resources. The potential for complete loss of confidentiality, integrity, and availability of the VPN service could also expose organizations to further attacks or data breaches if attackers leverage the disruption to conduct secondary attacks. Critical infrastructure, financial institutions, healthcare providers, and public sector entities relying on SonicWall SSL VPNs are particularly at risk. The disruption of remote access services could also impede incident response and recovery efforts during an attack, exacerbating the overall impact. Given the critical nature of the vulnerability and the lack of authentication requirements, attackers could launch automated attacks at scale, increasing the risk of widespread outages across multiple organizations.

Immediate mitigation should focus on reducing exposure of the SonicOS SSL VPN interface to untrusted networks. Organizations should restrict access to the VPN interface using network segmentation, firewall rules, and VPN gateway access control lists to allow connections only from trusted IP ranges. Enabling multi-factor authentication (MFA) and monitoring VPN access logs for anomalous activity can help detect exploitation attempts. Administrators should disable or limit SSL VPN services if feasible until a vendor patch is released. Applying virtual patching via intrusion prevention systems (IPS) or web application firewalls (WAF) that can detect and block format string attack patterns is recommended. Regular backups of device configurations and rapid incident response plans should be in place to restore services quickly if disruption occurs. Organizations should closely monitor SonicWall advisories for patch releases and apply updates promptly once available. Additionally, conducting internal vulnerability assessments and penetration testing focused on VPN infrastructure can help identify and remediate related weaknesses.