Is CVE-2026-87031 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-87031 being exploited in the wild.

How severe is CVE-2026-87031?

Low severity, with a CVSS score of 2.7, published 16 September 2026.

Which products and versions are affected?

Concrete CMS 9.2.0 through 9.5.3.

Is there a fix for CVE-2026-87031?

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-2026-87031 attacked?

It is attacked over the network.

Am I affected by CVE-2026-87031?

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-2026-87031: Concrete CMS REST API user creation permission bypass

CVE-2026-87031 · Severity: low · CVSS 2.7 · Published 2026-09-16

Concrete CMS, a web content management system, contains a vulnerability in its REST API user creation endpoint that fails to properly verify user permissions. This allows an attacker with a valid OAuth token to create new user accounts without administrative approval or email verification, potentially enabling them to modify website content and inject malicious code.

Technologies: Concrete CMS. Vendors: Concrete CMS.

Quick answers

Is CVE-2026-87031 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-87031 being exploited in the wild.
How severe is CVE-2026-87031?: Low severity, with a CVSS score of 2.7, published 16 September 2026.
Which products and versions are affected?: Concrete CMS 9.2.0 through 9.5.3.
Is there a fix for CVE-2026-87031?: 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-2026-87031 attacked?: It is attacked over the network.
Am I affected by CVE-2026-87031?: 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 exists in the POST /ccm/api/1.0/users endpoint (add() method in concrete/src/Api/Controller/Users.php) in Concrete CMS versions 9.2.0 through 9.5.3. The endpoint does not perform permission checks before creating user accounts, allowing any request carrying a valid OAuth token with the users:add scope—including client_credentials tokens with no user context—to create active, validated accounts. This bypasses email verification and administrator approval workflows. Under default registration settings, these accounts can edit page content, creating a stored cross-site scripting (XSS) attack vector and enabling further system compromise. Patches are available in versions after 9.5.3.

Affected products

Concrete CMS Concrete CMS 9.2.0 through 9.5.3

Timeline

2026-09-16: disclosed

References

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