CVE-2025-6775: Openvpn-cms-flask RCE Vulnerability

CVE-2025-6775 Overview

A critical command injection vulnerability has been discovered in xiaoyunjie openvpn-cms-flask versions up to 1.2.7. The vulnerability exists within the create_user function located in /app/api/v1/openvpn.py at the User Creation Endpoint. An attacker can exploit this flaw by manipulating the Username argument, enabling arbitrary command injection on the target system. The attack can be initiated remotely, and exploit details have been publicly disclosed.

Critical Impact

Remote attackers with low privileges can execute arbitrary commands on the server through the Username parameter in the User Creation Endpoint, potentially leading to full system compromise.

Affected Products

• xiaoyunjie openvpn-cms-flask versions up to 1.2.7

Discovery Timeline

• 2025-06-27 - CVE CVE-2025-6775 published to NVD
• 2026-01-30 - Last updated in NVD database

Technical Details for CVE-2025-6775

Vulnerability Analysis

This vulnerability is classified as a Command Injection (CWE-77) and Injection (CWE-74) flaw. The vulnerable component resides in the create_user function within the /app/api/v1/openvpn.py file, which handles user creation requests. The Username argument is not properly sanitized before being used in system commands, allowing attackers to inject malicious commands through this parameter.

The vulnerability requires network access and low-level privileges to exploit. An authenticated attacker can craft a malicious username containing shell metacharacters or command sequences that will be executed by the underlying operating system when the user creation process invokes system commands.

Root Cause

The root cause of this vulnerability is improper input validation and sanitization in the create_user function. When processing the Username argument, the application fails to adequately filter or escape special characters and command separators before passing the input to system-level operations. This allows attackers to break out of the intended command context and inject arbitrary commands.

Attack Vector

The attack can be initiated remotely over the network. An attacker with valid credentials (low privilege level required) can send a specially crafted HTTP request to the User Creation Endpoint (/app/api/v1/openvpn.py). By including command injection payloads within the Username parameter, such as shell metacharacters (;, |, &&, backticks, or $() command substitution), the attacker can execute arbitrary commands on the server with the privileges of the web application process.

The vulnerability mechanism involves unsanitized user input being passed directly to system command execution functions. When a malicious username is submitted, the application constructs a command string that includes the attacker-controlled input, which is then executed by the system shell. For detailed technical analysis and exploit information, refer to the GitHub Issue Discussion.

Detection Methods for CVE-2025-6775

Indicators of Compromise

• Unusual user creation requests with special characters in username fields (;, |, &&, backticks, $())
• Unexpected process spawning from the web application context
• System commands being executed by the web server process that are not part of normal operations
• Log entries showing malformed or suspicious usernames in authentication or user management logs

Detection Strategies

• Implement web application firewall (WAF) rules to detect command injection patterns in HTTP request parameters
• Monitor for anomalous process execution chains where the Python/Flask application spawns unexpected child processes
• Review application logs for failed or successful user creation attempts with suspicious username patterns
• Enable audit logging for system command execution and monitor for unexpected command invocations

Monitoring Recommendations

• Deploy endpoint detection and response (EDR) solutions to identify post-exploitation behavior
• Implement real-time alerting for command injection attack patterns targeting API endpoints
• Monitor network traffic for exfiltration attempts following potential exploitation
• Configure SIEM rules to correlate web application logs with system process execution events

How to Mitigate CVE-2025-6775

Immediate Actions Required

• Upgrade to openvpn-cms-flask version 1.2.8 or later immediately
• If immediate upgrade is not possible, restrict access to the User Creation Endpoint to trusted networks only
• Implement additional input validation at the web server or WAF level to block command injection patterns
• Review existing user accounts for evidence of compromise through malicious usernames

Patch Information

The vulnerability has been addressed in version 1.2.8 of openvpn-cms-flask. The fix is available in commit e23559b98c8ea2957f09978c29f4e512ba789eb6. Organizations should upgrade to the patched version immediately. The patch can be obtained from the GitHub Release v1.2.8 or by applying the security commit directly.

Workarounds

• Implement strict input validation on the Username parameter to allow only alphanumeric characters and safe symbols
• Deploy a reverse proxy with input filtering capabilities to sanitize requests before they reach the application
• Restrict network access to the User Creation Endpoint using firewall rules
• Run the application with minimal system privileges to limit the impact of successful exploitation

# Temporary mitigation - Restrict access to the vulnerable endpoint via nginx
location /app/api/v1/openvpn.py {
    allow 10.0.0.0/8;  # Allow only internal network
    deny all;
}