October CMS Vulnerable to Stored XSS via Branding Styles
Published 9 Jan 2026 · Updated 3 Feb 2026
Affected packages
- Affected
- <3.7.13
- Fixed in
- 3.7.13
composer require october/system:^3.7.13- Affected
- >=4.0.0 <4.0.12
- Fixed in
- 4.0.12
composer require october/system:^4.0.12Details
A cross-site scripting (XSS) vulnerabilities was identified in October CMS backend configuration forms:
- Branding and Appearances Styles
A user with the
Customize Backend Stylespermission could inject malicious HTML/JS into the stylesheet input at *Settings → Branding & Appearance → Styles*.
A specially crafted input could break out of the intended <style> context, allowing arbitrary script execution across backend pages for all users.
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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.
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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.
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Workarounds
If upgrading immediately is not possible:
- Restrict the permissions
Customize Backend Stylesto fully trusted administrators only.
This reduces exposure but does not fully eliminate risk.
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Credits
- Reported by Nakkouch Tarek
Is GHSA-wvpq-h33f-8rp6 in any of your client repos?
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References
Advisory data from OSV.dev (opens OSV.dev in a new tab), refreshed daily.