CVE-2025-4999 is a command injection vulnerability identified in the Linksys FGW3000-AH and FGW3000-HK devices running firmware versions up to 1.0.17.000000. The vulnerability resides in the HTTP POST request handler, specifically in the function sub_4153FC within the /cgi-bin/sysconf.cgi component. The flaw is triggered by manipulation of the 'supplicant_rnd_id_en' argument, which is not properly sanitized before being passed to system commands. This allows an attacker to inject arbitrary commands remotely without requiring authentication or user interaction. The vulnerability has been publicly disclosed, and although the vendor was notified early, no response or patch has been provided. The CVSS 4.0 score is 5.3 (medium severity), reflecting network attack vector, low attack complexity, no privileges or user interaction required, but limited impact on confidentiality, integrity, and availability. No known exploits are currently observed in the wild, but the public disclosure increases the risk of exploitation attempts. The vulnerability affects a range of firmware versions, indicating a broad exposure for devices running these versions. The lack of vendor response and patch availability increases the urgency for mitigation by users and administrators.

For European organizations, this vulnerability poses a significant risk primarily to those using Linksys FGW3000-AH or FGW3000-HK devices in their network infrastructure, especially in edge or gateway roles. Successful exploitation could allow remote attackers to execute arbitrary commands on affected devices, potentially leading to unauthorized control, data exfiltration, network pivoting, or disruption of services. Given the devices are often used in small to medium business or residential environments, compromised devices could be leveraged as entry points into corporate networks or as part of botnets. The medium CVSS score suggests limited direct impact on confidentiality, integrity, and availability, but the ease of exploitation without authentication raises concerns. European organizations relying on these devices for critical connectivity or security functions may face operational disruptions or data breaches. The absence of vendor patches means organizations must rely on network-level mitigations and device replacement strategies to reduce exposure. Additionally, the public disclosure increases the likelihood of targeted attacks within Europe, where these devices are deployed.

1. Immediate network segmentation: Isolate affected Linksys FGW3000-AH and FGW3000-HK devices from critical internal networks to limit potential lateral movement if compromised. 2. Disable remote management interfaces and restrict access to the device management interface to trusted IP addresses only. 3. Monitor network traffic for unusual command injection patterns or unexpected outbound connections originating from these devices. 4. Employ intrusion detection/prevention systems (IDS/IPS) with updated signatures to detect exploitation attempts targeting the 'supplicant_rnd_id_en' parameter. 5. Where possible, replace affected devices with alternative models or vendors that have confirmed patches or are not vulnerable. 6. If replacement is not immediately feasible, consider deploying firewall rules to block HTTP POST requests to /cgi-bin/sysconf.cgi or filter suspicious payloads. 7. Maintain up-to-date asset inventories to identify all affected devices and prioritize mitigation efforts. 8. Engage with Linksys support channels regularly for updates or potential patches, despite the current lack of response. 9. Educate IT staff about this vulnerability and ensure incident response plans include steps for potential exploitation scenarios involving these devices.