CVE-2023-23596: Nginx Proxy Manager RCE Vulnerability

CVE-2023-23596 Overview

CVE-2023-23596 is an OS command injection vulnerability affecting jc21 NGINX Proxy Manager through version 2.9.19. When creating an access list, the backend builds an htpasswd file with crafted username and/or password input that is concatenated without any validation, and is directly passed to the exec command. This design flaw potentially allows an authenticated attacker to execute arbitrary commands on the underlying system. It is important to note that this vulnerability is not part of any NGINX software shipped by F5.

Critical Impact

Authenticated attackers can achieve remote code execution on systems running vulnerable versions of NGINX Proxy Manager, potentially leading to complete system compromise, data theft, or lateral movement within the network.

Affected Products

• jc21 NGINX Proxy Manager versions up to and including 2.9.19
• Systems with access list functionality enabled
• Deployments allowing authenticated user input for access list creation

Discovery Timeline

• 2023-01-20 - CVE-2023-23596 published to NVD
• 2025-04-03 - Last updated in NVD database

Technical Details for CVE-2023-23596

Vulnerability Analysis

This vulnerability is classified as OS Command Injection (CWE-78), which occurs when an application constructs OS commands using externally-influenced input without proper neutralization. In the case of NGINX Proxy Manager, the access list functionality accepts user-supplied username and password values that are used to build htpasswd files. The backend code directly concatenates these user inputs into a command string that is subsequently passed to an exec function, creating an injection point for malicious commands.

The vulnerability is exploitable over the network and requires low privileges (authenticated user access). No user interaction is required for exploitation, and successful attacks can result in high impact to confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of CVE-2023-23596 lies in the improper handling of user input within the access-list.js backend component. Specifically, the code responsible for generating htpasswd entries fails to validate or sanitize the username and password fields before concatenating them into a shell command. This allows specially crafted input containing shell metacharacters or command separators to break out of the intended command context and execute arbitrary commands with the privileges of the NGINX Proxy Manager process.

Attack Vector

The attack is network-based and requires authentication to the NGINX Proxy Manager interface. An attacker with valid credentials can exploit this vulnerability through the following attack flow:

1. Authenticate to the NGINX Proxy Manager web interface
2. Navigate to the access list creation functionality
3. Craft a malicious username or password containing shell command injection payloads (e.g., command separators like ;, |, or $() constructs)
4. Submit the access list creation request
5. The backend processes the input without validation and executes the injected commands

The vulnerable code path is located in the backend's access-list.js file at the htpasswd generation logic. For technical details, see the GitHub NginxProxyManager Code Review and DW1 Security Advisory #57.

Detection Methods for CVE-2023-23596

Indicators of Compromise

• Unusual process spawning from the NGINX Proxy Manager backend process (Node.js)
• Unexpected outbound network connections originating from the Proxy Manager server
• Access list entries containing shell metacharacters such as ;, |, &&, ||, or $()
• Anomalous system commands in process logs following access list creation events

Detection Strategies

• Monitor the access-list.js execution context for abnormal child process creation using endpoint detection tools
• Implement web application firewall (WAF) rules to detect command injection patterns in access list API requests
• Review NGINX Proxy Manager logs for access list creation requests with suspicious username or password patterns
• Deploy SentinelOne Singularity to detect and block unauthorized command execution attempts

Monitoring Recommendations

• Enable detailed logging for the NGINX Proxy Manager application and monitor for command injection indicators
• Implement network segmentation to limit the blast radius of potential compromise
• Configure alerting for privilege escalation attempts or unexpected administrative actions on Proxy Manager hosts
• Regularly audit access list configurations for anomalous or suspicious entries

How to Mitigate CVE-2023-23596

Immediate Actions Required

• Upgrade NGINX Proxy Manager to a version newer than 2.9.19 that addresses this vulnerability
• Audit existing access list entries for signs of exploitation or malicious content
• Review user accounts with access to the Proxy Manager interface and revoke unnecessary privileges
• Consider placing the NGINX Proxy Manager behind additional authentication layers

Patch Information

Organizations should update to the latest version of jc21 NGINX Proxy Manager that includes fixes for this command injection vulnerability. Review the project's official repository and release notes for patched versions. For detailed information about the vulnerability, refer to DW1 Security Advisory #57.

Workarounds

• Restrict access to the NGINX Proxy Manager interface to trusted networks only using firewall rules
• Implement strong authentication and limit the number of users with access list creation privileges
• Deploy a reverse proxy or WAF in front of NGINX Proxy Manager to filter malicious input patterns
• Monitor and log all access list creation and modification activities for forensic analysis

# Example: Restrict NGINX Proxy Manager access to trusted IPs using iptables
iptables -A INPUT -p tcp --dport 81 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 81 -j DROP

# Example: Enable verbose logging for audit purposes
# Add to your NGINX Proxy Manager configuration
# Set LOG_LEVEL=debug in the container environment variables