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Medium

October CMS Vulnerable to Stored XSS via Branding Styles

  • Disclosed: 09.01.2026
  • Updated: 11.10.2026 10:22

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

Affected software

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PlatformPackageVulnerable versionsFixed in
Composer package october/system < 3.7.13, >= 4.0.0, < 4.0.12 3.7.13, 4.0.12

References

CVSS score 6.1/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N
Weakness (CWE)
CWE-79
Platform
Composer
Package
october/system
Disclosed
09.01.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-wvpq-h33f-8rp6 - CC BY 4.0

Vulnerability history: october/system

All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (25) in the archive
Total entries
25
First → latest
06.2020 09.2026
Without a fix
0
Exploited in attacks
1

Severity breakdown

  • Critical 1
  • High 8
  • Medium 9
  • Low 7

Disclosures per year

Severity:
  1. October CMS Vulnerable to Stored XSS via Branding Styles this entry
    Medium · 6.1 CVE-2025-61676 < 3.7.13, >= 4.0.0, < 4.0.12 3.7.13, 4.0.12
  2. October CMS safe mode bypass using Twig sandbox escape
    Critical · 9.1 CVE-2023-44382 >= 3.0.0, < 3.4.15 3.4.15
  3. October CMS Safe Mode bypass leads to authenticated Remote Code Execution
    High · 7.2 CVE-2022-35944 >= 2.0.0, < 2.2.34, >= 3.0.0, < 3.0.66 2.2.34, 3.0.66
  4. October CMS upload process vulnerable to RCE via Race Condition
    High · 8.1 CVE-2022-24800 < 1.0.476, >= 1.1.0, < 1.1.12, >= 2.0.0, < 2.2.15 1.0.476, 1.1.12, 2.2.15
  5. Authenticated remote code execution in October CMS
    High · 7.2 CVE-2022-21705 < 1.0.474, >= 1.1.0, < 1.1.10, >= 2.0.0, < 2.1.27 1.0.474, 1.1.10, 2.1.27
  6. october/system arbitrary code execution
    High · 8.8 CVE-2021-32650 >= 1.1.0, < 1.1.6, < 1.0.473 1.1.6, 1.0.473
  7. October/System authenticated file write leads to remote code execution
    High · 8.8 CVE-2021-32649 >= 1.1.0, < 1.1.6, < 1.0.473 1.1.6, 1.0.473
  8. Deleted Admin Can Sign In to Admin Interface
    High · 7.2 CVE-2021-41126 >= 2.1.0, < 2.1.12 2.1.12
  9. October CMS auth bypass and account takeover
    High · 7.4 CVE-2021-29487 < 1.0.472, >= 1.1.1, < 1.1.5 1.0.472, 1.1.5
  10. Account Takeover in Octobercms
    High · 8.2 Exploited in attacks CVE-2021-32648 < 1.0.472, >= 1.1.1, < 1.1.5 1.0.472, 1.1.5

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