CVE-2024-23827: Nginxui Nginx UI RCE Vulnerability

CVE-2024-23827 Overview

CVE-2024-23827 is a critical Path Traversal vulnerability affecting Nginx-UI, a web interface designed to manage Nginx configurations. The Import Certificate feature in Nginx-UI allows arbitrary file writes to the system due to insufficient input validation. The feature fails to verify whether the provided user input is actually a certificate or key file, enabling attackers to write malicious content to arbitrary paths on the target system. This vulnerability can be leveraged to achieve Remote Code Execution (RCE) by overwriting the application's configuration file (app.ini).

Critical Impact

Unauthenticated attackers can exploit this vulnerability to write arbitrary files to the system, potentially leading to complete server compromise through remote code execution.

Affected Products

• Nginx-UI versions 1.2.0 through 2.0.0.beta.11 (all releases and pre-release builds)
• Nginx-UI 1.9.9 and related patch versions (1.9.9-1 through 1.9.9-4)
• Nginx-UI 2.0.0 beta versions (beta1 through beta11, including patch variants)

Discovery Timeline

• 2024-01-29 - CVE-2024-23827 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-23827

Vulnerability Analysis

This Path Traversal vulnerability (CWE-22) exists in the Import Certificate functionality of Nginx-UI. The application provides a feature that allows administrators to import SSL/TLS certificates and private keys for managing Nginx HTTPS configurations. However, the implementation lacks proper validation of the file paths and content types provided by users.

The vulnerability allows an attacker to bypass intended directory restrictions and write files to arbitrary locations on the filesystem. Since the web interface typically runs with elevated privileges to manage Nginx configurations, the arbitrary write capability can be weaponized to overwrite critical system or application files.

Root Cause

The root cause of this vulnerability is the absence of input validation in the Import Certificate feature. The application fails to:

1. Verify that the uploaded content is actually a valid certificate or private key
2. Sanitize file path inputs to prevent directory traversal sequences
3. Restrict write operations to designated certificate storage directories

This allows attackers to supply path traversal sequences (such as ../) or absolute paths in the request, directing the file write operation to unintended locations on the filesystem.

Attack Vector

The attack can be executed remotely over the network without requiring authentication. An attacker can craft a malicious request to the Import Certificate endpoint, specifying a target path outside the intended certificate directory. The most impactful exploitation scenario involves overwriting the app.ini configuration file with attacker-controlled content.

By modifying the application configuration, attackers can:

• Change authentication settings to gain administrative access
• Modify execution parameters to inject malicious commands
• Alter service bindings to redirect traffic or enable additional attack vectors
• Configure the application to execute arbitrary code on startup

The vulnerability allows complete compromise of the Nginx-UI application and potentially the underlying server, depending on the permissions under which the service runs.

Detection Methods for CVE-2024-23827

Indicators of Compromise

• Unexpected modifications to the app.ini configuration file or other system files
• Web server logs showing requests to certificate import endpoints with unusual path parameters containing ../ sequences
• Unauthorized changes to Nginx configurations or SSL certificates
• New or modified files in unexpected system directories created by the Nginx-UI process

Detection Strategies

• Monitor file integrity for critical configuration files including app.ini and Nginx configuration directories
• Implement web application firewall (WAF) rules to detect path traversal patterns in HTTP requests
• Review access logs for the certificate import API endpoint for suspicious activity
• Deploy endpoint detection solutions to monitor for unexpected file write operations by the Nginx-UI process

Monitoring Recommendations

• Enable detailed logging for the Nginx-UI application and regularly audit log files for anomalous certificate import requests
• Configure file integrity monitoring (FIM) on critical system directories and the Nginx-UI installation path
• Monitor for process execution anomalies following any certificate import operations
• Set up alerts for configuration file modifications outside of scheduled maintenance windows

How to Mitigate CVE-2024-23827

Immediate Actions Required

• Upgrade Nginx-UI to version 2.0.0.beta.12 or later immediately
• If immediate upgrade is not possible, restrict network access to the Nginx-UI interface to trusted IP addresses only
• Review file system permissions and ensure Nginx-UI runs with minimal necessary privileges
• Audit the system for any signs of compromise, particularly checking for unauthorized file modifications

Patch Information

The vulnerability has been addressed in Nginx-UI version 2.0.0.beta.12. Users should upgrade to this version or later to remediate the vulnerability. The fix implements proper validation of certificate import requests to prevent arbitrary file write operations.

For detailed information about the security fix, refer to the GitHub Security Advisory.

Workarounds

• Implement network-level access controls to restrict access to the Nginx-UI interface to trusted networks or VPN connections only
• Place Nginx-UI behind a reverse proxy with additional authentication layers
• Temporarily disable the Import Certificate feature if not actively required
• Run Nginx-UI in a containerized environment with restricted filesystem access to limit the impact of potential exploitation

# Example: Restrict Nginx-UI access to localhost only via iptables
# Replace 8080 with your Nginx-UI port
iptables -A INPUT -p tcp --dport 8080 -s 127.0.0.1 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP