Source: cret@cert.org
The diagnostic-ping implementation on ZyXEL PMG5318-B20A devices with firmware before 1.00(AANC.2)C0 allows remote attackers to execute arbitrary commands via the PingIPAddr parameter.
Remote code execution (RCE) vulnerability exists in ZyXEL PMG5318-B20A devices, allowing attackers to execute arbitrary commands by manipulating the PingIPAddr parameter. This flaw enables complete compromise of the affected devices, potentially leading to network breaches and data theft. The vulnerability is easily exploitable, posing a significant risk to organizations using these devices.
Step 1: Target Identification: The attacker identifies a vulnerable ZyXEL PMG5318-B20A device with firmware before 1.00(AANC.2)C0 on the network. This can be achieved through network scanning or other reconnaissance techniques.
Step 2: Payload Delivery: The attacker crafts a malicious HTTP request to the device's diagnostic-ping endpoint. This request includes a crafted PingIPAddr parameter containing a command injection payload. For example, the payload might include a command to download and execute a reverse shell or create a user account.
Step 3: Command Execution: The vulnerable device processes the HTTP request. Due to the lack of input validation, the injected command within the PingIPAddr parameter is executed by the system.
Step 4: System Compromise: The injected command executes with the privileges of the web server or the system user, granting the attacker control over the device. This can lead to complete system compromise, including access to sensitive data, network access, and the ability to pivot to other systems on the network.
The vulnerability stems from insufficient input validation in the diagnostic-ping implementation. The PingIPAddr parameter, intended to specify an IP address for ping testing, is directly passed to a system command without proper sanitization. This lack of input validation allows attackers to inject arbitrary commands within the PingIPAddr parameter. The system then executes these injected commands with elevated privileges, leading to RCE. The root cause is a command injection vulnerability due to the insecure use of user-supplied input in a system call. Specifically, the code likely uses a function like system() or popen() without properly escaping or validating the input, allowing attackers to append malicious commands to the ping command.
While no specific APT groups are directly linked to this CVE, the ease of exploitation and potential impact make it attractive to various threat actors. Given the nature of the vulnerability, it's likely that this vulnerability has been used in botnet creation and for initial access. The device's age and the lack of updates make it a prime target. CISA KEV status is unknown based on the provided information, but should be investigated.
Monitor network traffic for suspicious HTTP requests to the diagnostic-ping endpoint (e.g., /diagnostic-ping).
Analyze HTTP request logs for unusual PingIPAddr parameter values, especially those containing shell metacharacters (e.g., ;, |, &, $, `).
Implement intrusion detection system (IDS) rules to identify command injection attempts based on known exploit patterns.
Monitor device logs for unexpected command executions or suspicious activity.
Check for the presence of unauthorized user accounts or backdoors on the device.
Upgrade the ZyXEL PMG5318-B20A firmware to version 1.00(AANC.2)C0 or later. This is the primary and most effective remediation.
If upgrading is not immediately possible, disable the diagnostic-ping functionality if not required. This reduces the attack surface.
Implement a web application firewall (WAF) to filter malicious requests, including command injection attempts.
Segment the network to limit the impact of a compromised device.
Regularly audit device configurations and logs for suspicious activity.
Change default credentials and enforce strong password policies.