CVE-2026-25939: FUXA Authorization Bypass Vulnerability

CVE-2026-25939 Overview

CVE-2026-25939 is a critical authorization bypass vulnerability affecting FUXA, a web-based Process Visualization (SCADA/HMI/Dashboard) software. This vulnerability allows an unauthenticated, remote attacker to create and modify arbitrary schedulers within the FUXA application. Given that FUXA is commonly deployed in industrial control system (ICS) and SCADA environments, successful exploitation could expose critical operational technology (OT) infrastructure to follow-on attacks, including unauthorized process manipulation and potential safety incidents.

Critical Impact

Unauthenticated remote attackers can manipulate scheduler configurations in ICS/SCADA environments, potentially disrupting industrial processes and enabling further compromise of connected control systems.

Affected Products

• FUXA version 1.2.8
• FUXA version 1.2.9
• FUXA version 1.2.10

Discovery Timeline

• 2026-02-09 - CVE CVE-2026-25939 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-25939

Vulnerability Analysis

This authorization bypass vulnerability (CWE-862: Missing Authorization) exists in FUXA's API handling for scheduler operations. The vulnerable versions fail to properly validate user authentication and authorization before allowing scheduler creation and modification operations. Specifically, the application does not adequately check whether the requesting user has sufficient privileges, allowing guest users or completely unauthenticated users to perform administrative actions on the scheduler subsystem.

The vulnerability is particularly dangerous in ICS/SCADA contexts because schedulers often control automated processes, triggering actions at predetermined times. An attacker who gains the ability to create or modify these schedulers could potentially orchestrate malicious automation sequences affecting physical processes.

Root Cause

The root cause lies in insufficient authorization checks within the FUXA API layer. The application failed to implement proper access controls for scheduler mutation operations, specifically not verifying whether the requesting user was a guest user or belonged to unauthorized groups before processing scheduler-related API requests.

Attack Vector

The attack can be executed remotely over the network without any authentication requirements. An attacker needs only network access to the FUXA web interface to exploit this vulnerability. The attack involves sending crafted API requests to scheduler endpoints, bypassing the intended authorization mechanisms to create or modify schedulers that control automated actions within the SCADA/HMI environment.

The security patch introduces a dedicated isGuestUser() function to properly identify and block guest users from performing scheduler mutations:

function isGuestUser(userId, userGroups) {
    if (userId === 'guest') {
        return true;
    }
    if (Array.isArray(userGroups) && userGroups.includes('guest')) {
        return true;
    }
    return false;
}

Source: GitHub Commit Details

Detection Methods for CVE-2026-25939

Indicators of Compromise

• Unexpected scheduler entries appearing in FUXA configuration that were not created by authorized administrators
• API requests to scheduler endpoints originating from unauthenticated sessions or guest user accounts
• Unusual automation sequences executing at unexpected times within the SCADA/HMI environment
• Log entries showing scheduler modifications without corresponding administrative login events

Detection Strategies

• Monitor FUXA API logs for scheduler-related endpoint requests (/api/scheduler) from unauthenticated or guest sessions
• Implement network intrusion detection rules to identify API calls targeting scheduler mutation operations
• Deploy application-layer firewall rules to inspect and alert on scheduler modification attempts from untrusted sources
• Enable comprehensive audit logging for all FUXA administrative operations

Monitoring Recommendations

• Establish baseline scheduler configurations and alert on any unauthorized changes
• Implement real-time alerting for scheduler API endpoint access patterns that deviate from normal administrative workflows
• Deploy SentinelOne agents on systems hosting FUXA to detect post-exploitation activities and lateral movement attempts
• Regularly review FUXA user accounts and permissions to identify unauthorized guest access configurations

How to Mitigate CVE-2026-25939

Immediate Actions Required

• Upgrade FUXA to version 1.2.11 or later immediately
• Restrict network access to FUXA instances using firewall rules, limiting connectivity to authorized management networks only
• Audit existing scheduler configurations for any unauthorized or suspicious entries
• Review FUXA logs for historical evidence of exploitation attempts

Patch Information

The FUXA development team has addressed this vulnerability in version 1.2.11. The patch implements proper guest user detection and blocks unauthorized access to scheduler mutation operations. Organizations should upgrade to version 1.2.11 or later by obtaining the patched release from the official FUXA GitHub repository. The specific security fix can be reviewed in the commit details.

Workarounds

• Place FUXA instances behind a reverse proxy with authentication requirements enforced at the proxy layer
• Implement network segmentation to isolate FUXA servers from untrusted networks
• Disable guest user functionality if not operationally required
• Deploy a web application firewall (WAF) to filter malicious API requests targeting scheduler endpoints

# Example: Restrict access to FUXA using iptables (Linux)
# Allow only specific management subnet to access FUXA port
iptables -A INPUT -p tcp --dport 1881 -s 10.10.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 1881 -j DROP