CVE-2021-31630: OpenPLC V3 Firmware RCE Vulnerability

CVE-2021-31630 Overview

CVE-2021-31630 is a command injection vulnerability in Open PLC Webserver v3 that allows remote attackers to execute arbitrary code via the "Hardware Layer Code Box" component on the /hardware page of the application. This vulnerability affects industrial control system (ICS) infrastructure, making it particularly concerning for operational technology (OT) environments.

Critical Impact

Remote attackers with low-privilege access can execute arbitrary commands on the underlying system, potentially compromising the entire PLC infrastructure and connected industrial processes.

Affected Products

• OpenPLC Project OpenPLC V3 Firmware
• OpenPLC Project OpenPLC V3 Hardware
• Open PLC Webserver v3

Discovery Timeline

• 2021-08-03 - CVE CVE-2021-31630 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-31630

Vulnerability Analysis

This command injection vulnerability (CWE-94: Improper Control of Generation of Code) exists in the Hardware Layer Code Box component of the Open PLC Webserver v3. The vulnerability allows authenticated users to inject malicious commands through the web interface that are subsequently executed on the underlying operating system with the privileges of the webserver process.

The flaw stems from insufficient input validation on user-supplied data within the /hardware page functionality. When a user submits code through the Hardware Layer Code Box, the application fails to properly sanitize the input before processing it, allowing command sequences to escape the intended context and execute arbitrary system commands.

Root Cause

The root cause of this vulnerability is improper input validation and sanitization in the Hardware Layer Code Box component. The application accepts user input intended for hardware configuration but does not adequately filter or escape special characters and command sequences. This allows attackers to inject shell commands that are executed by the underlying system when the hardware layer code is processed.

Attack Vector

The attack is network-based and requires low-privilege authentication to access the /hardware page. An attacker with valid credentials can navigate to the Hardware Layer Code Box component and inject malicious commands embedded within the input field. The injected commands are then executed when the hardware layer configuration is compiled or processed by the system.

The exploitation process involves submitting specially crafted input through the web interface that includes command injection payloads. Since the vulnerability requires only low-privilege access, any authenticated user could potentially exploit this flaw to gain code execution on the PLC system. Technical details and exploitation methodology are documented in the Packet Storm RCE Exploit and demonstrated in the YouTube Security Presentation.

Detection Methods for CVE-2021-31630

Indicators of Compromise

• Unusual or unexpected processes spawned by the OpenPLC webserver service
• Web server logs showing suspicious requests to the /hardware endpoint with encoded or special characters
• Unauthorized modifications to hardware layer configuration files
• Network connections initiated from the PLC system to external hosts

Detection Strategies

• Monitor web application logs for requests to /hardware containing shell metacharacters such as ;, |, $(), or backticks
• Implement web application firewall (WAF) rules to detect command injection patterns in POST requests to the hardware configuration endpoint
• Deploy endpoint detection to identify unusual child processes spawned by the webserver process
• Analyze network traffic for anomalous outbound connections originating from PLC systems

Monitoring Recommendations

• Enable detailed logging on the OpenPLC webserver to capture all requests to sensitive endpoints
• Implement file integrity monitoring on hardware layer configuration files and system binaries
• Set up alerts for any shell or command interpreter processes spawned by the OpenPLC application
• Monitor for privilege escalation attempts following initial webserver process compromise

How to Mitigate CVE-2021-31630

Immediate Actions Required

• Restrict network access to the OpenPLC webserver to trusted IP addresses and management networks only
• Implement strong authentication and limit user accounts with access to the /hardware configuration page
• Deploy network segmentation to isolate PLC systems from general enterprise networks
• Review and audit user access logs for any suspicious activity on the hardware configuration pages

Patch Information

Organizations should check the OpenPLC Project for updated firmware and software releases that address this vulnerability. Ensure all OpenPLC V3 installations are updated to the latest available version that includes security patches for command injection vulnerabilities.

Workarounds

• Implement input validation at the network perimeter using a web application firewall configured to block command injection patterns
• Disable or restrict access to the Hardware Layer Code Box functionality if not required for operations
• Run the OpenPLC webserver with minimal system privileges to limit the impact of successful exploitation
• Consider implementing application-layer access controls that require additional authorization for hardware configuration changes

# Network access restriction example using iptables
# Restrict access to OpenPLC webserver (default port 8080) to management network only
iptables -A INPUT -p tcp --dport 8080 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP