CVE-2025-4076 is a command injection vulnerability identified in the LB-LINK BL-AC3600 wireless router, affecting all firmware versions up to 1.0.22. The vulnerability resides in the function easy_uci_set_option_string_0 within the /cgi-bin/lighttpd.cgi component, specifically in the Password Handler module. The flaw arises from improper sanitization of the 'routepwd' argument, which an attacker can manipulate to inject arbitrary commands. This injection occurs remotely without requiring user interaction or authentication, making exploitation feasible over the network. The vulnerability has been publicly disclosed, and although no known exploits are currently observed in the wild, the availability of a public disclosure increases the risk of exploitation. The vendor has not responded to notifications regarding this issue, and no patches or mitigations have been released at this time. The CVSS v4.0 base score is 5.3, indicating a medium severity level, with attack vector being network-based, low attack complexity, no privileges or user interaction required, and limited impact on confidentiality, integrity, and availability. The vulnerability affects a widely deployed consumer and small office router model, which is often used as a gateway device in home and small business networks. Successful exploitation could allow an attacker to execute arbitrary commands on the device, potentially leading to full device compromise, network traffic interception, or pivoting to internal networks. Given the critical nature of command injection vulnerabilities and the lack of vendor response, this issue poses a significant risk to affected users and organizations relying on this hardware for network connectivity and security.

For European organizations, the exploitation of CVE-2025-4076 could lead to unauthorized remote code execution on LB-LINK BL-AC3600 routers, resulting in compromised network gateways. This could allow attackers to intercept, modify, or redirect network traffic, potentially exposing sensitive data or enabling lateral movement within corporate networks. Small and medium enterprises (SMEs) and home offices using these routers may be particularly vulnerable due to limited IT security resources and delayed patching capabilities. The compromise of network infrastructure devices can disrupt business operations, degrade network availability, and facilitate further attacks such as data exfiltration or deployment of malware. Additionally, the lack of vendor patches increases the window of exposure, forcing organizations to rely on network-level mitigations or device replacement. Given the router’s role in perimeter defense, successful exploitation could undermine the confidentiality, integrity, and availability of organizational data and services. The medium CVSS score reflects limited impact scope and partial impact on confidentiality and integrity, but the ease of remote exploitation without authentication elevates the threat level for organizations with these devices deployed.

Since no official patches or vendor responses are available, European organizations should implement the following specific mitigations: 1) Immediately identify and inventory all LB-LINK BL-AC3600 devices within the network. 2) Where possible, isolate these devices on segmented network zones with strict access controls to limit exposure to untrusted networks. 3) Disable remote management interfaces or restrict access to trusted IP addresses only, reducing the attack surface. 4) Employ network intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics to detect anomalous HTTP requests targeting /cgi-bin/lighttpd.cgi or suspicious command injection patterns. 5) Consider replacing vulnerable devices with alternative routers from vendors with active security support if mitigation is not feasible. 6) Monitor network traffic for unusual behavior indicative of compromise, such as unexpected outbound connections or command execution artifacts. 7) Educate users and administrators about the vulnerability and the importance of restricting access to router management interfaces. 8) Regularly review firewall rules and router configurations to ensure minimal exposure. These steps go beyond generic advice by focusing on network segmentation, access restriction, and active monitoring tailored to the specific vulnerability vector.