CVE-2025-40834 Overview
CVE-2025-40834 is a cross-site scripting (XSS) vulnerability in the Mendix RichText widget. The flaw affects all versions from V4.0.0 up to but not including V4.6.1. The widget fails to properly neutralize user-supplied input before rendering it, allowing an authenticated attacker to inject and execute malicious script content in a victim's browser session. The issue is tracked under CWE-79: Improper Neutralization of Input During Web Page Generation and was disclosed in Siemens Security Advisory SSA-190588.
Critical Impact
Successful exploitation enables client-side script execution, exposing session tokens, credentials, and sensitive data rendered within the Mendix application context.
Affected Products
- Mendix RichText widget versions V4.0.0 through V4.6.0
- Mendix applications embedding the vulnerable RichText widget
- Environments distributed via Siemens Mendix component channels
Discovery Timeline
- 2025-11-17 - CVE-2025-40834 published to the National Vulnerability Database
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-40834
Vulnerability Analysis
The Mendix RichText widget accepts formatted text input and renders it inside the Mendix application user interface. The widget does not properly sanitize or encode input before injecting it into the Document Object Model (DOM). An attacker with low-level application privileges can supply crafted content containing HTML or JavaScript payloads. When another user views the affected content, the browser parses and executes the injected script within the application's origin.
This is a stored or reflected XSS condition depending on how the affected application persists and renders RichText content. The CVSS 4.0 vector indicates the attack requires network access, low privileges, and user interaction. Only confidentiality of the vulnerable component is impacted, meaning integrity and availability are not directly affected by the primary attack.
Root Cause
The root cause is missing output neutralization inside the RichText rendering path. The widget trusts input passed through the rich-text editing pipeline and does not strip, encode, or filter dangerous constructs such as <script> tags, javascript: URIs, or event handler attributes like onerror and onload. This falls squarely within [CWE-79] behavior for improper HTML encoding.
Attack Vector
An authenticated user with permission to edit or submit RichText content crafts a payload embedding an executable script fragment. The payload is stored or reflected through the Mendix application and delivered to a victim through normal application flows. When the victim renders the page containing the payload, the browser executes the script in the application context. This grants the attacker access to session cookies, local storage tokens, and any data the victim can view. See the Siemens Security Advisory SSA-190588 for vendor details.
No verified public proof-of-concept code is available. The vulnerability mechanism is standard reflected or stored XSS through unsanitized rich-text markup rendered by the widget.
Detection Methods for CVE-2025-40834
Indicators of Compromise
- Unexpected <script> tags, on* event attributes, or javascript: URIs stored within Mendix entities backed by RichText fields
- Outbound HTTP requests from user browsers to attacker-controlled domains originating from Mendix application pages
- Session token exfiltration attempts appearing in web proxy or WAF logs correlated to Mendix application URLs
Detection Strategies
- Audit database records storing RichText content for HTML tags and JavaScript event handlers that fall outside the expected formatting set
- Deploy a web application firewall rule set to flag XSS payload patterns in requests targeting Mendix application endpoints
- Correlate authenticated user sessions with anomalous DOM-modifying activity observed in browser telemetry
Monitoring Recommendations
- Enable Content Security Policy (CSP) reporting to capture blocked inline script execution attempts
- Log and review all edits to RichText fields by users with content authoring privileges
- Monitor Mendix application access logs for repeated submissions containing encoded HTML entities and script fragments
How to Mitigate CVE-2025-40834
Immediate Actions Required
- Upgrade the Mendix RichText widget to version V4.6.1 or later in all affected applications
- Rebuild and redeploy Mendix applications after updating the widget dependency
- Review the RichText content store and remove any persisted payloads that contain script constructs
Patch Information
Siemens released the fix in Mendix RichText widget version V4.6.1. Application owners must update the widget dependency in their Mendix project and republish the application. Refer to Siemens Security Advisory SSA-190588 for the authoritative patch guidance and version matrix.
Workarounds
- Restrict RichText authoring permissions to trusted users until the patched widget is deployed
- Enforce a strict Content Security Policy that disallows inline scripts and untrusted script sources for Mendix application origins
- Apply server-side HTML sanitization on any content persisted through RichText inputs before rendering to other users
# Example Content-Security-Policy header for Mendix application responses
Content-Security-Policy: default-src 'self'; script-src 'self'; object-src 'none'; base-uri 'self'; frame-ancestors 'self'
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
