CVE-2025-8816 is a high-severity stack-based buffer overflow vulnerability affecting multiple Linksys range extender models, including RE6250, RE6300, RE6350, RE6500, RE7000, and RE9000, specifically in firmware versions up to 20250801. The vulnerability resides in the setOpMode function within the /goform/setOpMode endpoint. An attacker can manipulate the 'ethConv' argument to trigger a stack-based buffer overflow condition. This flaw allows remote attackers to execute arbitrary code or cause denial of service without requiring user interaction or authentication, as the vulnerable endpoint is accessible remotely. The vulnerability has been publicly disclosed, and although the vendor was notified early, no patch or response has been provided to date. The CVSS 4.0 base score is 8.7, reflecting the ease of exploitation (network attack vector, low complexity), no privileges or user interaction required, and high impact on confidentiality, integrity, and availability. The absence of vendor patches and the public disclosure increase the risk of exploitation, potentially enabling attackers to gain control over affected devices or disrupt network connectivity. The affected devices are commonly used as Wi-Fi range extenders in home and small office environments, but may also be deployed in enterprise branch offices or public Wi-Fi networks, expanding the attack surface. The vulnerability's exploitation could lead to network compromise, lateral movement, or persistent footholds within organizational networks.

For European organizations, this vulnerability poses significant risks, especially for those relying on Linksys range extenders in their network infrastructure. Exploitation could lead to unauthorized remote code execution, allowing attackers to intercept, manipulate, or disrupt network traffic. This can compromise sensitive data confidentiality and integrity, degrade network availability, and facilitate further attacks such as lateral movement or deployment of malware. Small and medium enterprises (SMEs) and public institutions using these devices without timely firmware updates are particularly vulnerable. The lack of vendor response and patches increases the likelihood of exploitation attempts, potentially impacting critical services and business continuity. Additionally, compromised extenders could be leveraged as entry points for broader attacks against corporate networks or public Wi-Fi users, raising concerns for privacy and regulatory compliance under GDPR and other European data protection laws.

Given the absence of official patches, European organizations should immediately implement compensating controls. These include isolating affected Linksys extenders on segmented network zones with strict access controls to limit exposure. Disable remote management interfaces or restrict access to trusted IP addresses only. Monitor network traffic for anomalous activity indicative of exploitation attempts targeting /goform/setOpMode endpoints. Employ intrusion detection/prevention systems (IDS/IPS) with updated signatures to detect buffer overflow exploit patterns. Where possible, replace vulnerable devices with models from vendors providing timely security updates. Conduct regular firmware audits and maintain an inventory of network devices to identify and remediate vulnerable units promptly. Educate IT staff about this specific threat to ensure rapid incident response. Finally, consider deploying network-level mitigations such as application-layer firewalls to block malicious payloads targeting the vulnerable parameter.