CVE-2025-9935 is a command injection vulnerability identified in the TOTOLINK N600R router, specifically affecting firmware version 4.3.0cu.7866_B20220506. The vulnerability resides in the function sub_4159F8 within the /web_cste/cgi-bin/cstecgi.cgi file. This CGI script is part of the router's web management interface. An attacker can exploit this vulnerability remotely without any authentication or user interaction by sending specially crafted requests to the vulnerable CGI endpoint. The flaw allows arbitrary command execution on the underlying operating system, potentially enabling full control over the device. The CVSS 4.0 base score is 6.9 (medium severity), reflecting the network attack vector, low attack complexity, no privileges or user interaction required, but limited impact on confidentiality, integrity, and availability. Although no known exploits are currently observed in the wild, the exploit code has been publicly disclosed, increasing the risk of exploitation. The vulnerability could be leveraged to disrupt network operations, intercept or manipulate traffic, or pivot to other internal systems if the router is part of a larger network infrastructure. The lack of authentication requirement and remote exploitability make this a significant risk for exposed devices, especially those accessible from the internet or untrusted networks.

For European organizations, this vulnerability poses a tangible risk to network security and operational continuity. TOTOLINK routers, including the N600R model, are used in various small to medium business environments and residential settings across Europe. Successful exploitation could lead to unauthorized access to network traffic, disruption of internet connectivity, or use of compromised routers as a foothold for further attacks within corporate networks. This is particularly concerning for organizations with remote or branch offices relying on these devices for internet access or VPN termination. Confidentiality could be compromised through interception or manipulation of data, while integrity and availability of network services could be degraded or lost. The medium severity rating suggests moderate impact, but the ease of exploitation and lack of authentication requirement elevate the threat level. European entities in sectors such as finance, healthcare, and critical infrastructure, where network reliability and data protection are paramount, could face operational and reputational damage if targeted.

Organizations should immediately verify if they deploy TOTOLINK N600R routers with the affected firmware version 4.3.0cu.7866_B20220506. If so, they should seek firmware updates or patches from TOTOLINK; if no official patch is available, consider upgrading to a newer, patched firmware version or replacing the device with a secure alternative. Network administrators should restrict access to the router’s web management interface by implementing network segmentation and firewall rules to limit access only to trusted internal IP addresses. Disabling remote management features or changing default management ports can reduce exposure. Monitoring network traffic for unusual requests to /web_cste/cgi-bin/cstecgi.cgi and implementing intrusion detection/prevention systems (IDS/IPS) with signatures for this vulnerability can help detect exploitation attempts. Additionally, organizations should conduct regular vulnerability assessments and penetration tests to identify exposed devices and validate mitigation effectiveness. Educating IT staff about this vulnerability and maintaining an inventory of network devices will aid in rapid response and remediation.