CVE-2026-25133: October CMS has Stored XSS via SVG Filter Bypass
A stored cross-site scripting (XSS) vulnerability was identified in the SVG sanitization logic. The regex pattern used to strip on event handler attributes could be bypassed using a crafted payload that exploits how the pattern matches attribute boundaries.
Impact - Stored XSS via malicious SVG files uploaded through the Media Manager - Could allow privilege escalation if a superuser views or embeds the malicious SVG - Requires authenticated backend access with media upload permissions (media.library.create) - SVG must be viewed or embedded in a page to trigger
Patches The vulnerability has been patched in v3.7.14 and v4.1.10. All users are encouraged to upgrade to the latest patched version.
Workarounds If upgrading immediately is not possible: - Disable SVG uploads by adding svg to the blocked extensions in media configuration - Set media.cleanvectors to true in configuration (enabled by default)
References - Reported by Offensive Security Research Team
Other sources
October is a Content Management System (CMS) and web platform. Versions prior to 3.7.14 and 4.1.10 contain a stored cross-site scripting (XSS) vulnerability in the SVG sanitization logic. The regex pattern used to strip event handler attributes (such as onclick or onload) could be bypassed using a crafted payload that exploits how the pattern matches attribute boundaries, allowing malicious SVG files to be uploaded through the Media Manager with embedded JavaScript. Exploitation could lead to privilege escalation if a superuser views or embeds the malicious SVG, and requires authenticated backend access with media upload permissions. The SVG must be viewed or embedded in a page for the payload to trigger. This issue has been fixed in versions 3.7.14 and 4.1.10.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/october/rainto a version that resolves this vulnerability.Fixed in 3.7.14 - Upgrade
Upgrade
composer/october/rainto a version that resolves this vulnerability.Fixed in 4.1.10 - Upgrade
Upgrade
October CMSto a version that resolves this vulnerability.Fixed in 3.7.14 - Upgrade
Upgrade
October CMSto a version that resolves this vulnerability.Fixed in 4.1.10 - Configuration
Set `media.clean_vectors` to `true` in the configuration (it is enabled by default) to mitigate stored XSS via SVG sanitization.
October CMS Media Manager/Media configuration media.clean_vectors = true - Configuration
Disable SVG uploads by adding `svg` to the blocked extensions in the media configuration.
October CMS media configuration (blocked extensions) blocked extensions = add `svg` to the blocked extensions
Event History
Frequently Asked Questions
What is the severity of CVE-2026-25133?
CVE-2026-25133 is classified as a medium severity vulnerability due to its potential impact on web application security.
How do I fix CVE-2026-25133?
To fix CVE-2026-25133, update your October CMS to version 3.7.14 or 4.1.10 or later.
What types of systems are affected by CVE-2026-25133?
CVE-2026-25133 affects October CMS versions prior to 3.7.14 and 4.1.10.
What type of vulnerability is CVE-2026-25133?
CVE-2026-25133 is a stored cross-site scripting (XSS) vulnerability due to inadequate sanitization of SVG elements.
Is there a workaround for CVE-2026-25133?
There is no officially documented workaround for CVE-2026-25133; upgrading to a patched version is recommended.