CVE-2023-26035: ZoneMinder Unauthenticated RCE Vulnerability

CVE-2023-26035 Overview

CVE-2023-26035 is a critical unauthenticated remote code execution vulnerability affecting ZoneMinder, a free and open source closed-circuit television (CCTV) software application for Linux. The vulnerability exists due to missing authorization checks on the snapshot action, which allows attackers to execute arbitrary commands on the underlying system without authentication.

ZoneMinder supports IP, USB, and Analog cameras and is widely deployed for video surveillance purposes. Versions prior to 1.36.33 and 1.37.33 are affected by this vulnerability, which stems from improper authorization controls that allow an attacker to bypass authentication and inject malicious commands that are subsequently executed via the shell_exec function.

Critical Impact

This vulnerability allows unauthenticated attackers to achieve remote code execution on systems running vulnerable ZoneMinder installations, potentially leading to complete system compromise of surveillance infrastructure.

Affected Products

• ZoneMinder versions prior to 1.36.33
• ZoneMinder versions prior to 1.37.33

Discovery Timeline

• 2023-02-25 - CVE-2023-26035 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-26035

Vulnerability Analysis

The vulnerability is classified as CWE-862 (Missing Authorization). The core issue lies in the snapshot action endpoint, which fails to implement proper authorization checks before processing requests. The snapshot functionality expects an id parameter to fetch an existing monitor configuration. However, due to insufficient input validation and authorization controls, an attacker can supply a crafted object instead of a legitimate monitor ID to create a new monitor with attacker-controlled parameters.

When the TriggerOn function is invoked, it passes the supplied Id parameter directly to shell_exec without proper sanitization. This allows an attacker to inject arbitrary shell commands that will be executed with the privileges of the ZoneMinder web server process, typically running as www-data or a similar service account.

The vulnerability requires no authentication, making it particularly dangerous for internet-exposed ZoneMinder installations. The attack can be executed entirely over the network with low complexity.

Root Cause

The root cause of this vulnerability is the absence of authorization checks on the snapshot action endpoint combined with insufficient input validation. The application fails to verify that the requesting user has appropriate permissions before processing the snapshot request. Additionally, the code does not properly validate that the supplied Id parameter is a legitimate monitor identifier rather than a malicious payload, allowing attackers to manipulate the control flow and inject commands into shell execution calls.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by sending a specially crafted HTTP request to the vulnerable snapshot endpoint. The attacker crafts a request that passes a malicious object instead of a valid monitor ID. When the application processes this request, the attacker-controlled data flows into the TriggerOn function, which ultimately calls shell_exec with the malicious payload, resulting in command execution on the target system.

The vulnerability allows attackers to execute arbitrary commands with the privileges of the web server user, potentially enabling them to establish persistence, exfiltrate sensitive surveillance footage, pivot to other systems on the network, or use the compromised system as part of a botnet.

Detection Methods for CVE-2023-26035

Indicators of Compromise

• Unusual HTTP requests to ZoneMinder snapshot endpoints containing unexpected object parameters instead of numeric IDs
• Web server error logs showing malformed requests to the snapshot action with shell metacharacters
• Unexpected child processes spawned by the ZoneMinder web application or Apache/Nginx worker processes
• Suspicious outbound network connections from the ZoneMinder server to unknown external hosts

Detection Strategies

• Monitor web application logs for requests to the snapshot endpoint containing non-numeric or object-type parameters
• Implement web application firewall (WAF) rules to detect and block requests containing shell metacharacters in the id parameter
• Use network intrusion detection systems to identify exploit attempts targeting the ZoneMinder snapshot functionality
• Deploy endpoint detection and response (EDR) solutions to monitor for anomalous command execution from web server processes

Monitoring Recommendations

• Enable verbose logging on ZoneMinder installations and forward logs to a centralized SIEM for analysis
• Implement file integrity monitoring on ZoneMinder installation directories to detect unauthorized modifications
• Monitor for unusual process execution chains originating from web server parent processes
• Set up alerts for any outbound connections from the ZoneMinder server that do not match expected camera or update traffic patterns

How to Mitigate CVE-2023-26035

Immediate Actions Required

• Upgrade ZoneMinder to version 1.36.33 or 1.37.33 or later immediately
• If immediate patching is not possible, restrict network access to the ZoneMinder web interface to trusted IP addresses only
• Place ZoneMinder behind a VPN or reverse proxy with strong authentication requirements
• Review system logs for any indicators of prior exploitation attempts

Patch Information

The vulnerability has been fixed in ZoneMinder versions 1.36.33 and 1.37.33. Organizations should update their ZoneMinder installations to these versions or later to remediate the vulnerability. The fix implements proper authorization checks on the snapshot action and validates input parameters to prevent command injection.

For detailed patch information and the security advisory, refer to the GitHub Security Advisory.

Workarounds

• Restrict access to the ZoneMinder web interface using firewall rules or network segmentation to limit exposure
• Implement a reverse proxy with authentication in front of ZoneMinder to add an additional layer of access control
• Disable the snapshot functionality if it is not required for your deployment until patching is complete
• Monitor the ZoneMinder server for suspicious activity and implement strict egress filtering to limit potential damage from exploitation

# Example: Restrict ZoneMinder access using iptables
# Allow only trusted network to access ZoneMinder web interface
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP