CVE-2024-0540 is a stack-based buffer overflow vulnerability identified in the Tenda W9 router, specifically version 1.0.0.7(4456). The flaw exists in the httpd component within the function formOfflineSet, where improper handling of the ssidIndex argument allows an attacker to overflow the stack buffer. This vulnerability can be exploited remotely without user interaction, requiring only low privileges (PR:L) on the device. The buffer overflow can lead to arbitrary code execution or cause denial of service by corrupting the stack, impacting confidentiality, integrity, and availability of the device. The vulnerability has been publicly disclosed, and although no known exploits are currently observed in the wild, the exploit code is available, increasing the risk of future attacks. The vendor, Tenda, was contacted but did not respond or provide a patch, leaving the vulnerability unmitigated. The CVSS v3.1 score is 6.3 (medium severity), reflecting network attack vector, low attack complexity, no user interaction, and partial impact on confidentiality, integrity, and availability. The vulnerability falls under CWE-121, a classic stack-based buffer overflow, which is a well-understood and dangerous class of bugs often leading to remote code execution.

For European organizations, the impact of this vulnerability depends on the deployment of Tenda W9 routers within their networks. If these devices are used in enterprise or critical infrastructure environments, exploitation could allow attackers to gain control over network gateways, leading to interception or manipulation of sensitive data, disruption of network services, or pivoting to internal systems. The remote exploitability without user interaction increases the risk of automated attacks or worm-like propagation. Confidentiality could be compromised by unauthorized access to network traffic, integrity could be undermined by malicious configuration changes or injection of malicious payloads, and availability could be affected by denial of service conditions caused by crashes or reboots. The lack of vendor response and patch availability exacerbates the risk, as organizations must rely on workarounds or device replacement. Given the medium CVSS score but critical classification by the reporter, organizations should treat this vulnerability seriously, especially those with exposed or poorly segmented network devices.

Since no official patch is available from Tenda, European organizations should implement the following specific mitigations: 1) Immediately identify and inventory all Tenda W9 devices running the affected firmware version 1.0.0.7(4456). 2) Isolate these devices from direct internet exposure by placing them behind firewalls or VPNs to limit remote access to the httpd service. 3) Restrict management interfaces to trusted internal networks and enforce strict access controls and network segmentation to minimize attack surface. 4) Monitor network traffic for unusual patterns or attempts to exploit the ssidIndex parameter, using intrusion detection systems with custom signatures if possible. 5) Consider replacing affected devices with models from vendors with active security support if mitigation is not feasible. 6) Regularly review and update network device firmware once a patch becomes available, and subscribe to vendor or vulnerability advisories for updates. 7) Employ network-level protections such as web application firewalls or reverse proxies to filter malicious payloads targeting the vulnerable function.