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 with firmware versions up to 20250801. The vulnerability resides in the setOpMode function within the /goform/setOpMode endpoint. Specifically, the flaw arises from improper handling of the ethConv argument, which can be manipulated remotely to trigger a stack-based buffer overflow. This type of vulnerability allows an attacker to overwrite the stack memory, potentially leading to arbitrary code execution, denial of service, or system compromise. The vulnerability is remotely exploitable without requiring user interaction or prior authentication, increasing the risk profile significantly. Although the vendor was notified early, no response or patch has been issued, and a public exploit has been disclosed, raising the likelihood of exploitation in the wild. The CVSS 4.0 score of 8.7 reflects the high impact on confidentiality, integrity, and availability, combined with ease of exploitation due to network attack vector and lack of required privileges or user interaction. The vulnerability affects a broad range of Linksys range extenders commonly used to extend wireless network coverage, which are often deployed in both home and enterprise environments. The absence of vendor mitigation or patch increases the urgency for affected organizations to implement compensating controls to reduce exposure.

For European organizations, this vulnerability poses a significant risk to network infrastructure security. Linksys range extenders are widely used in small to medium enterprises and home office setups, which are integral to corporate network connectivity. Exploitation could allow attackers to gain unauthorized control over network devices, enabling interception or manipulation of network traffic, lateral movement within internal networks, or disruption of wireless connectivity. This could lead to data breaches, loss of network availability, and compromise of sensitive information. The remote exploitability without authentication means attackers can target exposed devices directly from the internet or compromised internal networks. Given the lack of vendor response and patch, organizations face prolonged exposure, increasing the window for attackers to develop and deploy exploits. The impact is particularly critical for sectors relying on secure and stable network environments, such as finance, healthcare, and critical infrastructure. Additionally, compromised extenders could serve as footholds for further attacks against corporate networks or as part of botnets for broader cyber campaigns.

Since no official patch or vendor response is currently available, European organizations should take immediate and specific mitigation steps: 1) Identify and inventory all Linksys range extenders in use, focusing on the affected models and firmware versions. 2) Where possible, isolate these devices from direct internet exposure by placing them behind firewalls or network segmentation to limit remote access to the vulnerable /goform/setOpMode endpoint. 3) Disable or restrict remote management interfaces on the extenders to prevent unauthorized access. 4) Monitor network traffic for unusual activity or exploitation attempts targeting the ethConv parameter or the /goform/setOpMode endpoint. 5) Consider replacing vulnerable devices with alternative hardware from vendors with active security support if mitigation is not feasible. 6) Implement network intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics to detect exploitation attempts. 7) Educate IT staff about the vulnerability and ensure incident response plans include steps for this specific threat. 8) Regularly check for vendor updates or community-developed patches and apply them promptly once available.