Webmin is a web-based system administration tool for Unix/Linux servers, widely used by IT administrators to manage user accounts, services, and configurations through a browser interface. It simplifies tasks like file sharing, firewall setup, and software updates, making server management accessible even to less experienced users. Deployed in many enterprise environments, Webmin offers a centralized control panel for multiple servers.
CVE-2019-15107 is a critical OS command injection vulnerability in Webmin versions 1.882 through 1.920. The flaw resides in the password_change.cgi script, which fails to properly sanitize user-supplied input before passing it to shell commands. This allows an attacker to inject arbitrary operating system commands by crafting a malicious HTTP request.
The vulnerability is triggered by sending a POST request to /password_change.cgi with a specially crafted 'old' parameter. The script executes the 'passwd' command with the attacker-controlled input, enabling command injection. No authentication is required, making this a severe unauthenticated remote code execution flaw. The exploit is trivial to execute with tools like curl.
Successful exploitation grants the attacker full root-level access to the Webmin server. This can lead to complete system compromise, including data exfiltration, installation of backdoors, ransomware deployment, or lateral movement within the network. Given the CVSS score of 9.8, immediate patching is critical to prevent takeover.
- Upgrade Webmin to version 1.930 or later, which includes the official patch for CVE-2019-15107.
- If immediate upgrade is not possible, disable the password_change.cgi script by removing or renaming it in the Webmin installation directory.
- Restrict network access to the Webmin interface using a firewall, allowing only trusted IP addresses.
- Implement web application firewall (WAF) rules to block malicious requests targeting password_change.cgi.
- Enable detailed logging and monitor for unusual POST requests to /password_change.cgi with suspicious parameters.
- Conduct a thorough security audit of the Webmin server to detect signs of compromise, such as unauthorized user accounts or modified system files.
- Apply the principle of least privilege by limiting Webmin user permissions and using separate administrative accounts.
- Regularly review and update all server software to ensure timely patching of known vulnerabilities.
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