CVE-2025-41050: Apprain CMF Stored XSS Vulnerability

CVE-2025-41050 Overview

CVE-2025-41050 is a stored cross-site scripting (XSS) vulnerability in appRain CMF version 4.0.5. The flaw exists in the /apprain/developer/addons/update/base_libs endpoint, where the data[Addon][layouts] and data[Addon][layouts_except] parameters accept unsanitized user input. An authenticated attacker can inject JavaScript that persists in the application and executes in the browsers of subsequent users who view the affected content. The issue is tracked under [CWE-79] and was disclosed through INCIBE-CERT.

Critical Impact
An authenticated attacker with low privileges can store malicious scripts that execute against other users, enabling session theft, forced actions, and content manipulation within the appRain administrative interface.

Affected Products

appRain CMF 4.0.5
data[Addon][layouts] parameter in the addon update flow
data[Addon][layouts_except] parameter in the addon update flow

Discovery Timeline

2025-09-04 - CVE-2025-41050 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-41050

Vulnerability Analysis

The vulnerability is a stored XSS in the appRain content management framework. The developer-facing addon update handler at /apprain/developer/addons/update/base_libs accepts payloads containing the data[Addon][layouts] and data[Addon][layouts_except] fields. These fields are persisted without proper output encoding or input validation.

When an administrator or other authorized user renders a view that includes these stored values, the browser interprets the injected markup as executable script. This grants the attacker script execution within the victim's authenticated session context. Consequences include session token theft, cross-site request forgery on privileged actions, credential harvesting via injected forms, and defacement of administrative views.

Exploitation requires authentication with sufficient permissions to invoke the addon update endpoint, which limits the attack surface to users who can reach the developer interface.

Root Cause

The root cause is missing input validation and output encoding on two parameters handled by the addon update controller. User-controlled strings are stored and later rendered directly into HTML context, allowing arbitrary HTML and JavaScript to be echoed to viewers of the affected pages.

Attack Vector

The attack is delivered over the network against the appRain administrative surface. An authenticated attacker submits a crafted POST request to /apprain/developer/addons/update/base_libs containing a JavaScript payload in either data[Addon][layouts] or data[Addon][layouts_except]. The payload persists in the application backing store. When another authenticated user loads a page that renders the tainted field, the script executes with that user's privileges. For technical details, refer to the INCIBE-CERT advisory for appRain CMF.

Detection Methods for CVE-2025-41050

Indicators of Compromise

HTTP POST requests to /apprain/developer/addons/update/base_libs containing <script>, onerror=, onload=, or javascript: substrings in the data[Addon][layouts] or data[Addon][layouts_except] parameters.
Unexpected outbound requests from administrator browsers to attacker-controlled hosts following visits to addon management pages.
New or modified addon records containing HTML entities, encoded script tags, or SVG-based payloads in the layout fields.

Detection Strategies

Inspect web server and application logs for anomalous payloads submitted to the addon update endpoint, filtering on the two vulnerable parameter names.
Deploy a web application firewall rule that flags common XSS signatures in POST bodies targeting /apprain/developer/addons/.
Query the appRain database for stored addon records whose layouts or layouts_except columns contain HTML tags or JavaScript event handlers.

Monitoring Recommendations

Alert on administrative session activity that triggers outbound HTTP requests to previously unseen domains shortly after visiting developer pages.
Enable Content Security Policy (CSP) violation reporting to surface script execution attempts from unexpected sources.
Track authentication events for accounts with developer or administrator roles and correlate with modifications to addon configuration.

How to Mitigate CVE-2025-41050

Immediate Actions Required

Restrict access to the /apprain/developer/ path so only trusted administrators can reach the addon update controller.
Audit existing addon records for injected HTML or JavaScript in the layouts and layouts_except fields and remove any tainted entries.
Rotate session tokens and administrative credentials if evidence of exploitation is found.

Patch Information

No vendor patch is referenced in the NVD entry at the time of publication. Monitor the INCIBE-CERT advisory for appRain CMF and the appRain project channels for a fixed release. Until a patched version is available, apply compensating controls at the web server and application layers.

Workarounds

Place the appRain developer interface behind network-level access controls such as VPN or IP allowlisting.
Deploy a web application firewall rule that blocks HTML tags and JavaScript event handlers in the data[Addon][layouts] and data[Addon][layouts_except] parameters.
Enforce a strict Content Security Policy that disallows inline scripts and restricts script sources to reduce the impact of any successful injection.
Require reauthentication for privileged actions in the developer interface to limit the utility of a hijacked session.

bash

# Example nginx location restriction for the developer interface
location /apprain/developer/ {
    allow 10.0.0.0/8;
    deny all;
    add_header Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none'";
}