CVE-2026-82790: PC-HELPER Wireless I/O XSS Vulnerability

CVE-2026-82790 Overview

CVE-2026-82790 is a cross-site scripting (XSS) vulnerability [CWE-79] affecting Contec PC-HELPER Wireless I/O DIO-0404RY-LWF and DIO-0404RY-LWF-US devices. An authenticated attacker with low privileges can inject arbitrary script content that executes in the browser of a logged-in user who interacts with the affected interface. Successful exploitation allows the attacker to run arbitrary JavaScript in the victim's session context, potentially leading to configuration tampering or session abuse against these industrial I/O devices.

Critical Impact
Arbitrary script execution in a logged-in operator's browser can be leveraged to manipulate wireless I/O device configuration and compromise operational integrity of connected control systems.

Affected Products

Contec PC-HELPER Wireless I/O DIO-0404RY-LWF
Contec PC-HELPER Wireless I/O DIO-0404RY-LWF-US
Refer to the Contec Security Document for exact affected firmware versions

Discovery Timeline

2026-09-14 - CVE-2026-82790 published to NVD
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-82790

Vulnerability Analysis

The vulnerability is a stored or reflected cross-site scripting flaw in the web management interface of the DIO-0404RY-LWF wireless digital I/O modules. The affected interface fails to properly neutralize user-supplied input before rendering it in HTML output returned to authenticated users. When a logged-in user views the affected page, the injected payload executes in the context of their browser session.

Exploitation requires an authenticated session with low privileges and depends on user interaction, per the CVSS 4.0 vector. The scope of impact extends beyond the vulnerable component, since script execution occurs in the browser of a separate user. The EPSS probability of 0.138% indicates that active in-the-wild exploitation is currently unlikely.

Root Cause

The root cause is improper neutralization of input during web page generation [CWE-79]. The device firmware embeds attacker-controlled data into HTML responses without adequate output encoding or contextual escaping, allowing HTML and JavaScript payloads to be interpreted by the browser rather than rendered as inert text.

Attack Vector

An attacker with valid low-privilege credentials injects a JavaScript payload through an input field or parameter exposed by the device's web interface. When another authenticated user, such as an administrator, accesses the affected view, the browser executes the payload. The attacker can then exfiltrate session tokens, perform actions on behalf of the victim, or alter device configuration through authenticated API calls.

No verified public proof-of-concept exists at the time of publication. See the JVN Security Advisory JVNVU90314828 for additional technical detail.

Detection Methods for CVE-2026-82790

Indicators of Compromise

HTTP requests to the device management interface containing <script>, javascript:, onerror=, or encoded variants in parameter values
Unexpected outbound browser connections from operator workstations to attacker-controlled hosts after accessing the device UI
Unauthorized configuration changes on DIO-0404RY-LWF modules following administrative sessions

Detection Strategies

Inspect web server and reverse proxy logs for requests to the device with HTML or JavaScript metacharacters in query strings and form fields
Deploy Content Security Policy (CSP) violation reporting on management workstations to surface unauthorized inline script execution
Correlate authentication events on the device with subsequent anomalous configuration write operations

Monitoring Recommendations

Monitor network traffic between engineering workstations and DIO-0404RY-LWF devices for unusual payload patterns
Alert on new or unexpected user accounts created on affected devices, since XSS can be used to escalate access
Track browser process telemetry on OT operator hosts for anomalous child processes or credential access following device UI visits

How to Mitigate CVE-2026-82790

Immediate Actions Required

Restrict network access to the DIO-0404RY-LWF web interface to a dedicated management VLAN and trusted engineering hosts
Enforce strong, unique credentials on all device accounts and remove any unused low-privilege accounts that could be abused for injection
Instruct operators to log out of the device interface after use and avoid browsing untrusted content in the same browser session

Patch Information

Consult the Contec Security Document and the JVN Security Advisory JVNVU90314828 for the vendor's fixed firmware versions and update instructions. Apply the vendor-supplied firmware update to all affected DIO-0404RY-LWF and DIO-0404RY-LWF-US units.

Workarounds

Place the device behind a reverse proxy that strips or encodes HTML metacharacters in request parameters until patched firmware is deployed
Segment affected devices onto an isolated OT network with no direct access from user workstations or the internet
Use a dedicated hardened browser profile for device administration to limit the blast radius of any script execution

bash

# Example firewall restriction limiting device UI access to a management subnet
iptables -A INPUT -p tcp --dport 80 -s 10.10.20.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 10.10.20.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP