CVE-2025-9392 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 1.0.013.001, 1.0.04.001, 1.0.04.002, 1.1.05.003, and 1.2.07.001. The vulnerability resides in the qosClassifier function within the /goform/qosClassifier endpoint, where improper handling and validation of parameters such as dir, sFromPort, sToPort, dFromPort, dToPort, protocol, layer7, dscp, and remark_dscp can lead to a stack-based buffer overflow. This flaw can be exploited remotely without authentication or user interaction, as indicated by the CVSS vector (AV:N/AC:L/AT:N/UI:N/PR:L). The vulnerability allows an attacker to potentially execute arbitrary code with elevated privileges, compromising the confidentiality, integrity, and availability of the affected device. Despite early notification, Linksys has not responded or issued patches, and the exploit code has been publicly disclosed, increasing the risk of exploitation. The vulnerability's CVSS 4.0 score is 8.7 (high), reflecting its critical nature and ease of exploitation. The absence of vendor patches and public exploit availability make this a significant threat to networks relying on these devices for Wi-Fi extension and connectivity.

For European organizations, this vulnerability poses a substantial risk, especially for enterprises and small-to-medium businesses that deploy Linksys range extenders to improve wireless coverage. Successful exploitation can lead to full device compromise, enabling attackers to intercept or manipulate network traffic, launch further attacks within the internal network, or disrupt network availability. Given that these devices often operate at network edges or in less monitored segments, attackers could establish persistent footholds or pivot to more critical infrastructure. The lack of vendor response and patches increases the window of exposure. Additionally, organizations in sectors with stringent data protection requirements (e.g., finance, healthcare, government) face heightened risks of regulatory non-compliance and reputational damage if exploited. The remote, unauthenticated nature of the exploit means attackers can target vulnerable devices over the internet or local networks without user interaction, amplifying the threat landscape across European networks.

Immediate mitigation should focus on network-level controls and device isolation. Organizations should: 1) Identify and inventory all affected Linksys range extenders within their environment. 2) Restrict access to the management interfaces of these devices by implementing strict firewall rules limiting access to trusted IP addresses only. 3) Segment the network to isolate vulnerable extenders from critical systems and sensitive data. 4) Monitor network traffic for anomalous requests to /goform/qosClassifier or unusual port scanning activities targeting these devices. 5) Disable or restrict QoS features if possible, to reduce attack surface. 6) Where feasible, replace vulnerable devices with models from vendors with active security support. 7) Engage with Linksys support channels persistently to seek firmware updates or official patches. 8) Employ intrusion detection/prevention systems (IDS/IPS) signatures that detect exploitation attempts targeting this vulnerability. These steps go beyond generic advice by focusing on compensating controls and proactive detection in the absence of vendor patches.