CVE-2026-81921 In Concrete CMS 8.5.3 to 9,5,2, OAuth 2.0 Refresh-Token Grant Bypasses Account Status

Low 2.3 Published 15 Sep 2026 Updated 15 Sep 2026

Deactivated Concrete CMS users can retain API access because OAuth refresh tokens are not checked against account status.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-81921?

CVE-2026-81921 is a low-severity authentication bypass vulnerability in Concretecms Concrete Cms, published on 15 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Concrete CMS 8.5.3 through 9.5.2 enabled the OAuth 2.0 refresh-token grant using the unmodified upstream League grant, which issued new access tokens from a valid refresh token without re-checking the associated account's active status. A user who obtained a refresh token while active could therefore continue to mint valid access tokens after being deactivated or suspended (uIsActive=0), so deactivating an account did not revoke its API access. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 2.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:L/SC:L/SI:L/SA:L. Thanks sh4d0byss for reporting.

Weakness: CWE-862

Which versions are affected by CVE-2026-81921?

It affects 1 product.

Products include Concretecms Concrete Cms.

How do I fix CVE-2026-81921?

No fix has been published for CVE-2026-81921 yet. Limit exposure of the affected software until one is available.

Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.

Is CVE-2026-81921 being exploited?

There is no known exploitation of CVE-2026-81921 in the wild and no public exploit code.

All Concretecms Concrete Cms vulnerabilities

Sources

Also known as GHSA-46mx-9v73-g459.