CVE-2026-34791: Endian Firewall RCE Vulnerability

CVE-2026-34791 Overview

CVE-2026-34791 is a command injection vulnerability affecting Endian Firewall version 3.3.25 and prior. The vulnerability allows authenticated users to execute arbitrary OS commands via the DATE parameter in /cgi-bin/logs_proxy.cgi. The parameter value is used to construct a file path that is passed to a Perl open() call, which enables command injection due to incomplete regular expression validation.

Critical Impact

Authenticated attackers can achieve full system compromise through arbitrary OS command execution on the firewall appliance, potentially leading to network-wide security breaches.

Affected Products

• Endian Firewall version 3.3.25
• Endian Firewall versions prior to 3.3.25

Discovery Timeline

• 2026-04-02 - CVE-2026-34791 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-34791

Vulnerability Analysis

This vulnerability (CWE-78: Improper Neutralization of Special Elements used in an OS Command) exists in the log viewing functionality of Endian Firewall's web management interface. The /cgi-bin/logs_proxy.cgi CGI script accepts a DATE parameter that is intended to specify which log file to retrieve. However, the script uses this user-controlled input to construct a file path that is subsequently passed to Perl's open() function.

Perl's open() function with two arguments is known to be dangerous because it interprets special characters in the filename, including the pipe character (|), which allows command execution. While the developers implemented regular expression validation to sanitize the DATE parameter, the validation is incomplete, allowing attackers to bypass the check and inject malicious commands.

Root Cause

The root cause is insufficient input validation of the DATE parameter combined with unsafe use of Perl's two-argument open() function. The incomplete regular expression validation fails to account for all command injection vectors that Perl's open() interprets as special. This allows authenticated users to append or prepend shell commands that execute with the privileges of the web server process, typically running as root or with elevated permissions on firewall appliances.

Attack Vector

The attack requires network access to the Endian Firewall web management interface and valid user credentials (low privilege authentication is sufficient). An attacker constructs a malicious HTTP request to /cgi-bin/logs_proxy.cgi with a specially crafted DATE parameter containing shell metacharacters. When processed by the vulnerable Perl script, the injected commands execute on the underlying operating system.

For example, an attacker could leverage pipe characters or other shell metacharacters that bypass the incomplete validation to execute commands such as reverse shells, create backdoor accounts, or exfiltrate sensitive firewall configuration data. Technical details are available in the VulnCheck Advisory on Endian Firewall.

Detection Methods for CVE-2026-34791

Indicators of Compromise

• Unusual HTTP requests to /cgi-bin/logs_proxy.cgi containing pipe characters (|), backticks, or shell metacharacters in the DATE parameter
• Unexpected processes spawned by the web server or CGI processes
• Anomalous outbound network connections originating from the firewall appliance
• Unauthorized user accounts or SSH keys added to the system
• Modified system files or suspicious cron jobs on the Endian Firewall

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block requests containing command injection patterns in CGI parameters
• Configure log monitoring to alert on access to /cgi-bin/logs_proxy.cgi with unusual DATE parameter values
• Deploy endpoint detection and response (EDR) solutions to monitor for unexpected command execution on the firewall
• Enable verbose logging on the Endian Firewall web interface and forward logs to a SIEM for analysis

Monitoring Recommendations

• Monitor web server access logs for requests to /cgi-bin/logs_proxy.cgi with parameters containing special characters
• Set up alerts for any process execution originating from Perl CGI scripts that is not part of normal firewall operations
• Track outbound connections from the firewall to detect potential reverse shell or data exfiltration attempts
• Regularly audit user accounts and authentication logs on the Endian Firewall for unauthorized access

How to Mitigate CVE-2026-34791

Immediate Actions Required

• Restrict access to the Endian Firewall web management interface to trusted IP addresses only
• Review and limit user accounts with access to the web interface, applying principle of least privilege
• Implement network segmentation to isolate the firewall management interface from general user traffic
• Monitor for exploitation attempts while awaiting a vendor patch
• Consider deploying a reverse proxy with WAF capabilities in front of the management interface

Patch Information

At the time of publication, no official patch has been confirmed. Organizations should monitor the Endian Community Support portal for security updates and apply patches immediately when available. Review the VulnCheck Advisory on Endian Firewall for the latest vulnerability information.

Workarounds

• Restrict access to the web management interface by IP address using firewall rules or ACLs
• Disable access to /cgi-bin/logs_proxy.cgi if log viewing functionality through the web interface is not required
• Implement a web application firewall to filter requests containing command injection patterns
• Use VPN access for management interface, removing direct network exposure
• Consider temporary migration to an alternative firewall solution if the functionality is critical

# Example: Restrict management interface access via iptables
# Allow only trusted management network to access web interface
iptables -A INPUT -p tcp --dport 443 -s 192.168.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP

# Block direct access to vulnerable CGI script (if not needed)
# Add to web server configuration or use mod_rewrite/nginx location blocks