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Finding and Exploiting CVE-2025-50674 in OpenMediaVault

CVE-2025-50674

Introduction

Recently, I discovered a critical vulnerability in OpenMediaVault, a popular open-source network-attached storage solution. The vulnerability (published as CVE-2025-50674) allows authenticated users to escalate privileges to root via a newline injection attack. An attacker can exploit this vulnerability to change the root password, gaining complete system access and control over all data stored on the device.

In this post, I'll show you how I found this vulnerability, explain the technical details of the flaw, and walk through the exploitation process. I'll also provide the vulnerable code and discuss why this represents a significant security risk.

Details of the Vulnerability

The vulnerability exists in the password change functionality of OpenMediaVault. The issue is located in the changePassword() method of the User class which fails to validate user input before writing it to a temporary file that is passed to the Linux chpasswd command.

The vulnerable code is defined in /usr/share/php/openmediavault/system/user.inc:

public function changePassword($password) {
    if (empty($password)) {
        throw new \OMV\ValueException(
            "No password has been supplied for user '%s'.",
            $this->getName());
    }
    $tmpFile = new \OMV\System\TmpFile();
    $tmpFile->write(sprintf("%s:%s", $this->getName(), $password));
    $cmd = new \OMV\System\Process("chpasswd");
    $cmd->setInputFromFile($tmpFile->getFilename());
    $cmd->setRedirect2to1();
    $cmd->execute();
}

Let's break down the code execution flow:

  1. The method receives a $password parameter from user input via the API
  2. It performs a simple check to ensure the password is not empty
  3. It creates a temporary file using the TmpFile class, which generates a unique random filename in /tmp/
  4. It writes the string username:password to this file
  5. It creates a new Process object for the chpasswd Linux command
  6. It configures the process to take input from the temporary file
  7. It executes the command, which reads the temporary file and changes the password

The problem is clear - the $password variable is not sanitized before being written to the temporary file. The function only checks if the password is empty, but doesn't validate its content. Since the Linux chpasswd command processes each line in the input file as a separate password change operation in the format username:password, an attacker can inject a newline character followed by "root:newpassword" into the password field to change the root password as well.

How chpasswd Works

The chpasswd command is a Linux utility that allows for batch password updates. It reads from standard input or a file, processing each line in the format username:password. Each line results in a password change for the specified user. The command is typically executed with root privileges, allowing it to modify any user's password in the system.

When executed, chpasswd performs the following steps:

  1. Reads each line from input
  2. Parses the line to extract username and password
  3. Uses PAM (Pluggable Authentication Modules) to update the user's password
  4. Updates the shadow file with the new password hash

What makes this vulnerability particularly dangerous is that it allows a regular user to escalate privileges to root, giving complete control over the system with minimal effort.

Discovery Process

I discovered this vulnerability while performing security research on OpenMediaVault. After logging into the web interface with a regular user account, I began testing the password change functionality as this type of feature often processes sensitive information and interacts with system commands.

Using Burp Suite to intercept and analyze the HTTP requests, I noticed that the password change request was sending the new password directly to the backend through an API endpoint. The API call structure was:

POST /rpc.php HTTP/1.1
Host: openmediavault.local
Content-Type: application/json

{"service":"UserMgmt","method":"setPasswordByContext","params":{"password":"legitimatepassword"}}

Looking at the source code (OpenMediaVault is open-source), I traced the API call flow:

  1. The request is processed by the API controller
  2. The controller validates the user session/authentication
  3. The user object is loaded with the specified username
  4. The changePassword() method is called with the password from the request

Examining the changePassword() method, I immediately spotted the potential for newline injection due to:

  1. No input validation on the password parameter
  2. Direct use of the password in a system command
  3. The use of chpasswd which processes input line-by-line

The lack of input validation, combined with the use of the chpasswd command which processes input line by line, created the perfect conditions for a privilege escalation attack.

Technical Exploitation Details

Newline Injection Mechanics

The exploitation leverages how the Linux chpasswd command processes its input file. When OpenMediaVault's password change function is called, it:

  1. Creates a temporary file with a name like /tmp/omv_XXXXXX where XXXXXX is a random string
  2. Writes username:password to the file
  3. Passes the file to the chpasswd command using its standard input

The chpasswd command reads the file line by line, treating each line as a separate password change operation. By injecting a newline character into the password, we can add additional lines to be processed by chpasswd.

Privilege Escalation Mechanism

This vulnerability provides a direct privilege escalation path because any authenticated user can change the password of any other user, including root, by injecting a specially crafted payload. The attack works because:

  1. The changePassword() method fails to validate the password content
  2. The chpasswd command processes each line in the input file as a separate operation
  3. The command runs with root privileges as part of the OpenMediaVault system processes
  4. No additional authorization check is performed within the chpasswd utility itself - it simply processes all lines from its input

Payload Structure and Analysis

The malicious payload follows this structure:

legitimatepassword\nroot:maliciouspassword

Let's analyze what happens when this payload is processed:

  1. The system creates a temporary file (e.g., /tmp/omv_a1b2c3)
  2. The payload is written to the file, resulting in the following content: 
    regular_user:legitimatepassword
root:maliciouspassword
  3. The chpasswd command is executed with root privileges: sudo chpasswd < /tmp/omv_a1b2c3
  4. The command processes each line, changing:
    • The password for regular_user to legitimatepassword
    • The password for root to maliciouspassword

When processed:

  • legitimatepassword becomes the new password for the original user
  • root:maliciouspassword creates a new entry that changes the root password to maliciouspassword

Exploitation Process Using Burp Suite

Here's a detailed step-by-step guide to exploiting the vulnerability:

  1. I logged into OpenMediaVault with a regular user account
  2. Navigated to the password change functionality in the web interface
  3. Started a password change request for my user account
  4. Intercepted the request with Burp Suite's proxy
  5. Modified the password parameter to include a newline injection:
POST /api/v1/user/password HTTP/1.1
Host: openmediavault.local
Content-Type: application/json
Cookie: OMV_AUTH=abcdef123456

{
  "username": "regular_user",
  "password": "legitimatepassword\nroot:EvilRootPass"
}

The injection works because the JSON parser in PHP correctly interprets the escaped newline character (\n) as an actual newline in the resulting string.

When sent, the request successfully changed both the regular user's password and the root password. I confirmed the exploit worked by:

  1. Verifying my regular user account's password had changed to "legitimatepassword"
  2. Attempting to log in via SSH as root using "EvilRootPass"
  3. Examining the system logs which showed two password change events

Real-World Attack Scenario

In a real attack, an adversary would:

  1. Gain initial access to OpenMediaVault with a regular user account (through legitimate access, credential stuffing, or social engineering)
  2. Use the privilege escalation vulnerability to change the root password
  3. Log in as root and gain complete control over the storage device
  4. Access all data stored on the NAS
  5. Install persistent backdoors
  6. Potentially pivot to other systems on the network

This vulnerability is particularly concerning for internet-exposed OpenMediaVault instances, as attackers could gain full control of the storage system and all its data with minimal effort after obtaining any user-level account.

Mitigation

To fix this vulnerability, proper input validation needs to be implemented in the changePassword() method. A simple solution is to reject passwords containing newline characters:

// Validate password - reject if it contains newlines
if (preg_match('/[\r\n]/', $password)) {
    throw new \OMV\ValueException(
        "Password contains invalid characters for user '%s'.",
        $this->getName());
}

The OpenMediaVault team has addressed this vulnerability in newer versions by implementing proper input validation to prevent newline injections.

Conclusion

This vulnerability in OpenMediaVault demonstrates how seemingly small validation oversights can lead to critical security issues. The combination of unsanitized user input and interaction with system commands created a perfect storm for privilege escalation.

What makes this vulnerability particularly interesting is that it follows a classic pattern of injection attacks, yet it was overlooked during development and code review. It serves as a reminder that basic input validation is critical, especially when handling sensitive operations like password changes.

From a defensive perspective, the key lessons are:

  1. Always validate all user input, especially when used in system commands
  2. Follow the principle of least privilege for system operations
  3. Use secure APIs instead of shell commands whenever possible
  4. Implement proper authorization checks for sensitive functions

Keep your OpenMediaVault installations updated, and consider implementing network segmentation to limit access to these devices, especially from untrusted networks. Regular security audits of even trusted open-source software are essential to identify these types of vulnerabilities before attackers do.

References