CVE-2025-8820 is a high-severity stack-based buffer overflow vulnerability affecting multiple Linksys Wi-Fi range extender models, including RE6250, RE6300, RE6350, RE6500, RE7000, and RE9000, up to firmware version 20250801. The vulnerability resides in the wirelessBasic function within the /goform/wirelessBasic endpoint. Specifically, the flaw arises from improper handling of the submit_SSID1 argument, which can be manipulated by an attacker to overflow the stack buffer. This overflow can lead to arbitrary code execution or cause the device to crash, potentially resulting in denial of service. The vulnerability is remotely exploitable without authentication or user interaction, increasing its risk profile. The CVSS 4.0 score is 8.7 (high), reflecting the ease of remote exploitation and the significant impact on confidentiality, integrity, and availability. Despite early vendor notification, Linksys has not responded or released patches, and public exploit code has been disclosed, raising the likelihood of exploitation in the wild. The affected devices are commonly deployed in home and small office environments to extend wireless coverage, but their compromise could serve as a foothold for lateral movement into corporate networks or as part of botnets for broader attacks.

For European organizations, the impact of this vulnerability can be substantial. Many small and medium enterprises (SMEs) and home offices in Europe rely on Linksys range extenders to improve Wi-Fi coverage. Exploitation could allow attackers to execute arbitrary code on these devices, leading to network compromise, interception of sensitive data, or disruption of network services. Given the devices' role as network infrastructure components, attackers could pivot from compromised extenders to internal corporate networks, bypassing perimeter defenses. This risk is heightened in sectors with remote or hybrid workforces prevalent in Europe. Additionally, the lack of vendor patches increases exposure duration, and public exploit availability lowers the barrier for attackers. The vulnerability could also be leveraged in large-scale botnet campaigns affecting European internet infrastructure or critical services.

Since no official patches are available, European organizations should implement immediate compensating controls. These include isolating affected Linksys extenders on segmented network zones with strict access controls to limit lateral movement. Disable remote management interfaces if enabled, and restrict access to the /goform/wirelessBasic endpoint via firewall rules or network-level filtering. Regularly monitor network traffic for unusual activity originating from these devices. Organizations should consider replacing vulnerable devices with models from vendors that provide timely security updates. Additionally, implement network intrusion detection systems (NIDS) tuned to detect exploitation attempts targeting this vulnerability. Educate users and IT staff about the risks and signs of compromise. Finally, maintain an inventory of all network devices to ensure vulnerable models are identified and managed appropriately.