Is CVE-2026-85386 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-85386 being exploited in the wild.

How severe is CVE-2026-85386?

Medium severity, with a CVSS score of 6.1, published 16 September 2026.

Is there a fix for CVE-2026-85386?

A patch was published on 2026-09-16: Fixed in version 9.5.4 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-85386 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-85386?

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.

CVE-2026-85386: Concrete CMS stored XSS via XML file upload in Form Block

CVE-2026-85386 · Severity: medium · CVSS 6.1 · Published 2026-09-16

Concrete CMS, a content management platform, failed to properly validate XML and XSLT files uploaded through public form components. An attacker could upload a malicious XML file containing references to external stylesheets, which would execute JavaScript when an authenticated administrator viewed the file in a browser. If the victim was an admin, the attacker's script could perform administrative actions such as creating unauthorized user accounts.

Technologies: Concrete CMS. Vendors: Concrete CMS.

Quick answers

Is CVE-2026-85386 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-85386 being exploited in the wild.
How severe is CVE-2026-85386?: Medium severity, with a CVSS score of 6.1, published 16 September 2026.
Which products and versions are affected?: Concrete CMS before 9.5.4.
Is there a fix for CVE-2026-85386?: A patch was published on 2026-09-16: Fixed in version 9.5.4 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-85386 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-85386?: 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 cross-site scripting (XSS) flaw in the Form Block file-upload feature. XML documents were validated only by file extension and stored as publicly accessible files served inline from the application origin. An attacker could craft an XML document with an xml-stylesheet processing instruction pointing to an attacker-controlled XSLT stylesheet on the same origin. When a victim (especially an authenticated administrator) opened the file directly in a browser, the browser fetched and processed the stylesheet, executing embedded JavaScript in the Concrete CMS origin with the victim's privileges. The vulnerability required an unauthenticated attacker to upload the malicious file and a victim to interact with it. The issue was resolved in version 9.5.4.

Affected products

Concrete CMS Concrete CMS before 9.5.4

Timeline

2026-09-16: disclosed
2026-09-16: patched: Fixed in version 9.5.4

References

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