GHSA-gxxc-m74c-f48x: October CMS Vulnerable to Stored XSS via Editor and Branding Styles

A cross-site scripting (XSS) vulnerabilities was identified in October CMS backend configuration forms:

• Editor Settings Markup Styles
  A user with the Global Editor Settings permission could inject malicious HTML/JS into the stylesheet input at
  Settings → Editor Settings → Markup Styles.

A specially crafted input could break out of the intended <style> context, allowing arbitrary script execution across backend pages for all users.

Impact

• Persistent XSS across the backend interface.
• Exploitable by lower-privileged accounts with the above permissions.
• Potential consequences include privilege escalation, session hijacking, and execution of unauthorized actions in victim sessions.

Patches

The vulnerability has been patched in v4.0.12 and v3.7.13.
Stylesheet inputs are now sanitized to prevent injection of arbitrary HTML/JS.

All users are strongly encouraged to upgrade to the latest patched version.

Workarounds

If upgrading immediately is not possible:

• Restrict the permissions Global Editor Settings to fully trusted administrators only.

This reduces exposure but does not fully eliminate risk.

Credits

• Reported by Nakkouch Tarek

References

• GHSA-gxxc-m74c-f48x