Is CVE-2026-81901 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-81901 being exploited in the wild.

How severe is CVE-2026-81901?

High severity, with a CVSS score of 8.7, published 14 September 2026.

Which products and versions are affected?

Concrete CMS 9.2.0 through 9.5.2.

Is there a fix for CVE-2026-81901?

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-2026-81901 attacked?

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

Am I affected by CVE-2026-81901?

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-2026-81901: Concrete CMS REST API authorization bypass in page update endpoint

CVE-2026-81901 · Severity: high · CVSS 8.7 · Published 2026-09-14

Concrete CMS is a popular open-source content management system used to build and manage websites. A vulnerability in its REST API allows users with basic content-editing permissions to modify page properties, templates, and types—and crucially, to inject unescaped JavaScript into page headers that executes for all visitors, including administrators. An attacker could use this to steal credentials from reviewers or take over the site.

Technologies: Concrete CMS. Vendors: Concrete CMS.

Quick answers

Is CVE-2026-81901 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-81901 being exploited in the wild.
How severe is CVE-2026-81901?: High severity, with a CVSS score of 8.7, published 14 September 2026.
Which products and versions are affected?: Concrete CMS 9.2.0 through 9.5.2.
Is there a fix for CVE-2026-81901?: 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-2026-81901 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-81901?: 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 REST API endpoint PUT /ccm/api/1.0/pages/{cID} fails to enforce authorization checks on page-property, page-template, and page-type modifications. A user with only content-editing rights can bypass these checks via the REST API and set the header_extra_content attribute, which is rendered unescaped into the HTML head element. This allows persistent cross-site scripting (XSS) that affects all page visitors. The vulnerability requires HTTP network access to the API and a user account with content-editing permissions, but no additional user interaction is needed for the injected script to execute in visitors' browsers. A patch is available in Concrete CMS 9.5.3 and later.

Affected products

Concrete CMS Concrete CMS 9.2.0 through 9.5.2

Timeline

2026-09-14: disclosed

References

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