CVE-2026-25787: Motion Control Diagnostics XSS Vulnerability

CVE-2026-25787 Overview

CVE-2026-25787 is a stored Cross-Site Scripting (XSS) vulnerability [CWE-79] affecting the web interface of Siemens products that expose a "Motion Control Diagnostics" page. The flaw stems from improper validation and sanitization of Technology Object (TO) names rendered on that page. An authenticated attacker authorized to download a Totally Integrated Automation (TIA) project into the device can inject malicious scripts through a crafted TO name. When a legitimate user with appropriate rights browses the diagnostics page, the injected payload executes inside their authenticated web session.

Critical Impact
Script execution in an operator's authenticated session can be used to manipulate diagnostics data, hijack the session, or pivot deeper into industrial control workflows.

Affected Products

Siemens products exposing the "Motion Control Diagnostics" web interface (refer to Siemens advisory SSA-688146 for the authoritative product and version list)
Devices accepting TIA project downloads containing Technology Objects
Specific affected CPE entries are not enumerated in the NVD record at publication time

Discovery Timeline

2026-05-12 - CVE-2026-25787 published to NVD
2026-05-12 - Last updated in NVD database

Technical Details for CVE-2026-25787

Vulnerability Analysis

The vulnerability is a stored XSS issue classified under [CWE-79], Improper Neutralization of Input During Web Page Generation. The affected web interface accepts Technology Object names from TIA project artifacts and renders them on the "Motion Control Diagnostics" page without proper output encoding or input sanitization. An attacker with the privilege required to download a TIA project into the product can embed JavaScript or HTML control characters within a TO name. The payload is persisted on the device and rendered every time an authorized user views the diagnostics page.

Because the script executes within the victim's authenticated session, the attacker inherits the victim's effective permissions in the web interface. In an operational technology environment, this can include the ability to view sensitive process information, modify configuration through additional authenticated requests, or chain into further attacks against the engineering workflow.

Root Cause

The root cause is the absence of contextual output encoding when rendering attacker-controllable TO names in the HTML response. The device trusts data originating from TIA projects, treating project authors as fully trusted producers of safe content. This trust assumption breaks when a privileged but malicious user authors or modifies a project before download.

Attack Vector

The attack vector is network-based but requires high privileges and user interaction. The attacker must already hold credentials sufficient to download a TIA project, then craft a TO name containing an XSS payload. Exploitation completes when a separate authorized user opens the "Motion Control Diagnostics" page in a browser. Technical exploitation details beyond this behavior are not published; consult the Siemens Security Advisory SSA-688146 for vendor-specific guidance.

Detection Methods for CVE-2026-25787

Indicators of Compromise

Technology Object names containing HTML control characters such as <, >, ", or script tags within TIA project metadata.
Unexpected JavaScript execution, redirects, or DOM modifications observed when engineers access the "Motion Control Diagnostics" page.
TIA project downloads to devices originating from accounts that do not typically perform engineering changes.

Detection Strategies

Inspect TIA project archives prior to deployment for TO names that deviate from the organization's naming convention or include non-alphanumeric content.
Review web server and application logs on affected devices for anomalous responses or errors associated with the diagnostics page.
Correlate project download events with subsequent diagnostics page access by privileged accounts to identify suspicious sequences.

Monitoring Recommendations

Capture and retain authentication and project-download audit events from affected Siemens devices in a centralized log platform.
Monitor browser console errors and content security policy violations reported by engineering workstations interacting with device web interfaces.
Alert on creation or modification of Technology Objects with names containing scripting syntax or unusual encoding.

How to Mitigate CVE-2026-25787

Immediate Actions Required

Apply the fixes and follow remediation steps published in Siemens Security Advisory SSA-688146 as soon as updates are available for your affected product version.
Restrict the user accounts authorized to download TIA projects to a minimum, vetted set of engineers.
Require multi-factor authentication and strong credential hygiene for any account with engineering rights on affected devices.

Patch Information

Siemens has published advisory SSA-688146 covering this issue. Affected product versions, fixed firmware releases, and any temporary mitigations are listed in the Siemens Security Advisory SSA-688146. Apply the corresponding firmware update for each affected device family.

Workarounds

Limit network access to the device web interface to a dedicated engineering network segment protected by firewall rules.
Avoid browsing the "Motion Control Diagnostics" page from accounts with elevated privileges until patches are applied.
Enforce code review of TIA project changes, validating Technology Object names against an allowlist of safe characters before deployment.

bash

# Configuration example: restrict access to device web interface using host firewall rules
# Replace 10.10.20.0/24 with your authorized engineering subnet and <device-ip> with the device address
iptables -A INPUT -p tcp --dport 443 -s 10.10.20.0/24 -d <device-ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -d <device-ip> -j DROP