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Stored XSS via Branding Styles

Moderate
daftspunk published GHSA-wvpq-h33f-8rp6 Jan 9, 2026

Package

composer october/system (Composer)

Affected versions

<=3.7.12, <=4.0.11

Patched versions

3.7.13, 4.0.12

Description

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

  • Branding and Appearances Styles
    A user with the Customize Backend Styles permission 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.

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 Customize Backend Styles to fully trusted administrators only.

This reduces exposure but does not fully eliminate risk.

Credits

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
High
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N

CVE ID

CVE-2025-61676

Weaknesses

No CWEs

Credits