# CVE-2026-81927: Concrete CMS stored XSS in SVG file handling

Source: https://junglewise.ai/threats/cve-2026-81927-concrete-cms-stored-xss-in-svg-file-handling  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-15. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-81927 · Severity: medium · CVSS 5.4 · Published 2026-09-15

Concrete CMS, a content management system, contains a stored cross-site scripting vulnerability in its SVG file upload feature. When configured in a non-default "reject" mode, the system fails to properly sanitize SVG files, allowing an attacker with file upload permissions to inject malicious code that executes in the browsers of any user who views the uploaded file. This could lead to unauthorized account access, data theft, or malware distribution.

Technologies: [Concrete CMS](https://junglewise.ai/threats/technologies/concrete-cms). Vendors: [Concrete CMS](https://junglewise.ai/threats/vendors/concrete-cms).

## Quick answers

**Is CVE-2026-81927 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-81927 being exploited in the wild.

**How severe is CVE-2026-81927?** Medium severity, with a CVSS score of 5.4, published 15 September 2026.

**Which products and versions are affected?** Concrete CMS before 9.5.3.

**Is there a fix for CVE-2026-81927?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-81927 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-81927?** Check whether you run Concrete CMS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a stored XSS flaw in SVG file handling when the svg_sanitization.action is set to "reject" mode. The vulnerability exists because the sanitization logic only checks against a small built-in blocklist (script element and on* event handlers) but discards the results of the broader enshrined/svg-sanitize library, allowing vectors like javascript: URIs in xlink:href attributes to pass through unstripped. An authenticated user with file upload privileges can upload a malicious SVG file containing JavaScript code, which will execute in the browser context of any user who directly opens the file. The default "sanitize" mode is not affected. A patch is available in Concrete CMS version 9.5.3 and later.

## Affected products

- Concrete CMS Concrete CMS before 9.5.3

## Timeline

- 2026-09-15: disclosed

## References

- [https://github.com/concretecms/concretecms](https://github.com/concretecms/concretecms)
- [https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes](https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes)

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