CVE-2024-40890 is a command injection vulnerability classified under CWE-78, found in the CGI program of the Zyxel VMG4325-B10A DSL CPE firmware version 1.00(AAFR.4)C0_20170615 and earlier. The vulnerability arises from improper neutralization of special elements in OS commands, allowing an authenticated attacker to send a specially crafted HTTP POST request to execute arbitrary operating system commands on the device. This post-authentication requirement means the attacker must first gain valid credentials or leverage other means to authenticate. The vulnerability affects the device's management interface, which is typically accessible via HTTP. Exploitation can lead to full compromise of the device, enabling attackers to manipulate device configurations, intercept or redirect network traffic, or cause denial of service. The CVSS v3.1 score of 8.8 reflects high impact on confidentiality, integrity, and availability, with network attack vector, low attack complexity, and no user interaction required beyond authentication. No official patches or firmware updates have been linked yet, and no known exploits are publicly reported. The device is a legacy DSL CPE, commonly deployed in residential and small business environments, often forming the network edge. The vulnerability's exploitation could facilitate lateral movement or persistent footholds within affected networks.

For European organizations, this vulnerability poses a significant risk especially for those relying on Zyxel VMG4325-B10A devices in their network infrastructure. Successful exploitation could lead to unauthorized control over network edge devices, resulting in interception or manipulation of sensitive data, disruption of internet connectivity, or use of compromised devices as pivot points for further attacks. Given the device's role in DSL broadband connectivity, critical services and business operations could be impacted by denial of service or data breaches. The confidentiality of internal communications could be compromised, and integrity of network configurations undermined. Small and medium enterprises, as well as residential users in Europe, may be particularly vulnerable due to the legacy nature of the device and potential lack of timely firmware updates. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially if attackers develop targeted exploits. The impact is compounded in environments where network segmentation is weak or where device management interfaces are exposed to untrusted networks.

Organizations should first verify if Zyxel VMG4325-B10A devices are in use and identify firmware versions. Since no official patches are currently linked, mitigation should focus on reducing exposure: restrict access to device management interfaces to trusted internal networks only, preferably via VPN or secure management VLANs. Enforce strong authentication mechanisms and change default credentials to prevent unauthorized access. Monitor device logs for suspicious POST requests or unusual command executions. Consider network segmentation to isolate legacy DSL CPE devices from critical infrastructure. If possible, replace affected devices with newer models that have updated firmware and security features. Employ intrusion detection systems to flag anomalous HTTP POST traffic targeting management interfaces. Educate users and administrators about the risks of credential compromise and enforce regular password changes. Maintain an inventory of network devices to ensure timely identification of vulnerable hardware. Finally, stay alert for vendor advisories or patches addressing this vulnerability.