CVE-2025-5624 is a critical stack-based buffer overflow vulnerability found in the D-Link DIR-816 router, specifically version 1.10CNB05. The flaw resides in the QoSPortSetup function within the /goform/QoSPortSetup endpoint. By manipulating certain parameters—port0_group, port0_remarker, ssid0_group, and ssid0_remarker—an attacker can overflow the stack buffer. This vulnerability is remotely exploitable without requiring authentication or user interaction, making it highly dangerous. The overflow can lead to arbitrary code execution, potentially allowing an attacker to take full control of the affected device. The CVSS 4.0 score is 9.3 (critical), reflecting the high impact on confidentiality, integrity, and availability, combined with ease of exploitation. Notably, the affected product is no longer supported by D-Link, and no official patches are available. Although no known exploits are currently observed in the wild, the public disclosure of the exploit code increases the risk of imminent attacks. The vulnerability affects only the specific firmware version 1.10CNB05 of the DIR-816 router, which is a consumer-grade networking device commonly used in home and small office environments. The lack of vendor support and patch availability significantly increases the threat level, as vulnerable devices remain exposed indefinitely unless mitigated by other means.

For European organizations, this vulnerability poses a significant risk, especially for small businesses and home offices that rely on the D-Link DIR-816 router for internet connectivity and network segmentation. Successful exploitation can lead to complete compromise of the router, enabling attackers to intercept, modify, or disrupt network traffic, launch further attacks within the internal network, or use the device as a foothold for persistent access. Confidential data could be exposed or manipulated, network integrity compromised, and availability disrupted through denial-of-service conditions or malicious reconfiguration. The lack of vendor support means organizations cannot rely on official firmware updates, increasing the likelihood of prolonged exposure. This is particularly critical for sectors with sensitive data or regulatory compliance requirements (e.g., GDPR), as compromised network devices can lead to data breaches and legal consequences. Additionally, the exploitability without authentication and user interaction means attackers can scan and compromise vulnerable devices en masse, potentially leading to large-scale botnet formation or coordinated attacks against European infrastructure.

Given the absence of official patches, European organizations and users should take immediate alternative measures: 1) Replace the affected D-Link DIR-816 devices with newer, supported models that receive regular security updates. 2) If replacement is not immediately feasible, isolate the vulnerable router from the internet by disabling remote management features and restricting access to trusted internal networks only. 3) Employ network segmentation to limit the impact of a compromised device, ensuring critical systems are on separate VLANs or subnets. 4) Monitor network traffic for unusual activity indicative of exploitation attempts, such as unexpected connections to the /goform/QoSPortSetup endpoint or anomalous parameter usage. 5) Use intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics targeting this vulnerability once available. 6) Educate users about the risks and encourage regular review of device firmware and configurations. 7) Consider deploying firewall rules to block suspicious inbound traffic targeting the router's management interfaces. These steps go beyond generic advice by focusing on compensating controls and network architecture adjustments to mitigate risk in the absence of vendor patches.