CVE-2026-25893: FUXA Auth Bypass Vulnerability

CVE-2026-25893 Overview

CVE-2026-25893 is a critical authentication bypass vulnerability in FUXA, a web-based Process Visualization (SCADA/HMI/Dashboard) software. Prior to version 1.2.10, an unauthenticated remote attacker can gain administrative access via the heartbeat refresh API and execute arbitrary code on the server. This vulnerability poses a significant risk to industrial control systems and SCADA environments where FUXA is deployed.

Critical Impact

Unauthenticated remote attackers can gain full administrative access to FUXA installations and achieve arbitrary code execution on the underlying server, potentially compromising entire industrial control networks.

Affected Products

• FUXA versions prior to 1.2.10
• Web-based SCADA/HMI/Dashboard deployments using vulnerable FUXA versions
• Industrial control system environments running unpatched FUXA installations

Discovery Timeline

• 2026-02-09 - CVE-2026-25893 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-25893

Vulnerability Analysis

This authentication bypass vulnerability (CWE-285: Improper Authorization) exists in the heartbeat token refresh mechanism within FUXA's API layer. The flaw allows unauthenticated users to obtain valid authentication tokens through the heartbeat endpoint, effectively bypassing the entire authentication system. Once an attacker obtains a valid token, they gain full administrative privileges to the SCADA/HMI system, including the ability to execute arbitrary code on the server.

The vulnerability is particularly dangerous in industrial environments where FUXA manages process visualization and control systems. Successful exploitation could lead to unauthorized manipulation of industrial processes, data exfiltration, or complete system compromise.

Root Cause

The root cause lies in improper authorization checks within the heartbeat token refresh API endpoint in server/api/index.js. The vulnerable code path allowed token refresh operations to proceed without first verifying that the requesting user was properly authenticated. The req.isAuthenticated flag was not being checked before issuing new tokens, allowing guest users to receive valid authentication tokens that should only be issued to authenticated users.

Attack Vector

The attack leverages the network-accessible heartbeat API endpoint. An unauthenticated attacker can send crafted requests to the heartbeat endpoint with specific parameters to trigger the token refresh logic. Since the vulnerable code did not validate authentication status before issuing new tokens, the attacker receives a valid JWT token granting administrative access.

The following patch demonstrates the fix implemented in version 1.2.10:

                     res.end();
                 } else if (res.statusCode === 403) {
                     runtime.logger.error("api post heartbeat: Tocken Expired");
-                } else if (req.body.params) {
-                    const token = authJwt.getNewToken(req.headers)
-                    if (token) {
-                        res.status(200).json({
-                            message: 'tokenRefresh',
-                            token: token
+                }
+                if (req.body.params) {
+
+                    if (!req.isAuthenticated) {
+                        // guest → NON puo rinnovare token
+                        return res.status(200).json({
+                            message: 'guest'
                         });
-                    } else {
-                        res.end();
                     }
-                } else if (req.userId === 'guest') {
-                    res.status(200).json({
+
+                    const token = authJwt.getNewTokenFromRequest(req);
+                    return res.status(200).json({
+                        message: 'tokenRefresh',
+                        token
+                    });
+                }
+

Source: GitHub Commit

The corresponding JWT helper modifications ensure proper authentication state tracking:

             if (err) {
                 req.userId = "guest";
                 req.userGroups = ["guest"];
-            } else {
-                req.userId = decoded.id;
-                req.userGroups = decoded.groups;
-                if (req.headers['x-auth-user']) {
-                    let user = JSON.parse(req.headers['x-auth-user']);
-                    if (user && user.groups != req.userGroups) {
-                        res.status(403).json({ error: "unauthorized_error", message: "User Profile Corrupted!" });
-                    }
-                }
+                req.isAuthenticated = false;
+                return next();
             }
-            next();
+            req.userId = decoded.id;
+            req.userGroups = decoded.groups;
+            req.isAuthenticated = true;
+            return next();
         });
     } else {
         // notice that no token was provided...}
         req.userId = null;
         req.userGroups = null;
-        // if (secureEnabled) {
-        //     res.status(401).json({ error: "unauthorized_error", message: "Token missing!" });
-        // }
-        next();
+        return next();

Source: GitHub Commit

Detection Methods for CVE-2026-25893

Indicators of Compromise

• Unexpected authentication tokens being issued to unauthenticated sessions
• Anomalous API requests to the /api/heartbeat endpoint from external IP addresses
• Administrative actions performed by accounts that should not have elevated privileges
• Unusual patterns of token refresh requests without corresponding login events

Detection Strategies

• Monitor web server access logs for requests to heartbeat API endpoints from unauthenticated sources
• Implement anomaly detection for token issuance patterns that deviate from normal user behavior
• Deploy web application firewalls (WAF) to inspect and log API traffic to FUXA endpoints
• Audit authentication logs for discrepancies between login events and active sessions

Monitoring Recommendations

• Enable detailed logging for all authentication-related API endpoints in FUXA
• Configure SIEM rules to alert on token refresh operations without prior successful authentication
• Implement network segmentation monitoring to detect unauthorized access attempts to SCADA systems
• Establish baseline metrics for normal heartbeat API usage and alert on deviations

How to Mitigate CVE-2026-25893

Immediate Actions Required

• Upgrade FUXA installations to version 1.2.10 or later immediately
• Restrict network access to FUXA instances using firewall rules and network segmentation
• Audit existing user accounts and tokens for signs of unauthorized access
• Review server logs for any historical exploitation attempts

Patch Information

The vulnerability has been addressed in FUXA version 1.2.10. The fix introduces proper authentication state tracking via the req.isAuthenticated flag and ensures that token refresh operations are only permitted for authenticated users. Guest users now receive a 'guest' message response instead of valid authentication tokens.

For detailed patch information, refer to:

• GitHub Security Advisory
• GitHub Commit fe82348

Workarounds

• Deploy a reverse proxy with authentication in front of FUXA to add an additional authentication layer
• Implement network-level access controls to restrict access to FUXA only from trusted IP ranges
• Disable or block external access to the heartbeat API endpoint at the network perimeter
• Consider deploying SentinelOne Singularity for endpoint protection and runtime threat detection on FUXA servers

# Example: Restrict FUXA access using iptables (temporary mitigation)
# Allow only trusted management network to access FUXA
iptables -A INPUT -p tcp --dport 1881 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 1881 -j DROP