CVE-2025-13943 is an OS command injection vulnerability classified under CWE-78, affecting the Zyxel EX3301-T0 firmware versions up to 5.50(ABVY.7)C0. The flaw exists in the log file download functionality, where insufficient neutralization of special characters in user-supplied input allows an authenticated attacker to inject and execute arbitrary operating system commands on the device. This vulnerability requires the attacker to have valid credentials (post-authentication) but does not require any additional user interaction. The vulnerability is remotely exploitable over the network, as the affected function is accessible via the device’s management interface. The CVSS v3.1 base score is 8.8, indicating a high severity with network attack vector, low attack complexity, and privileges required but no user interaction. Successful exploitation compromises confidentiality, integrity, and availability, potentially allowing attackers to manipulate device configurations, intercept or alter data, disrupt device operations, or pivot into internal networks. No public exploits have been reported yet, but the vulnerability’s nature and impact make it a critical concern for affected organizations. The lack of available patches at the time of reporting necessitates interim mitigations.

The vulnerability allows attackers with valid credentials to execute arbitrary OS commands on Zyxel EX3301-T0 devices, leading to full compromise of the device. This can result in unauthorized access to sensitive information, manipulation or deletion of logs and configurations, disruption of network services, and potential lateral movement within the network. Organizations relying on these devices for network connectivity or security functions could face significant operational disruptions and data breaches. The high severity and network accessibility increase the risk of targeted attacks, especially in environments where device credentials are weak or reused. The absence of known exploits currently reduces immediate risk but does not diminish the potential for future exploitation. The impact extends to confidentiality, integrity, and availability, making this a critical threat to enterprise and service provider networks using affected Zyxel firmware.

1. Monitor Zyxel’s official channels for firmware updates addressing CVE-2025-13943 and apply patches promptly once released. 2. Restrict access to the device management interface to trusted IP addresses or VPNs to reduce exposure. 3. Enforce strong, unique authentication credentials and consider multi-factor authentication if supported. 4. Regularly audit and monitor device logs for suspicious activities, especially around log file download operations. 5. Disable or limit the log file download functionality if not essential or replace it with secure alternatives. 6. Segment network zones to isolate management interfaces from general user networks. 7. Employ intrusion detection/prevention systems to detect anomalous command injection attempts targeting Zyxel devices. 8. Educate administrators on the risks of post-authentication vulnerabilities and the importance of credential security. These steps help mitigate risk until official patches are available and reduce the attack surface.