CVE-2026-81921CWE-862broken-access-control

CVE-2026-81921

Medium · published September 15, 2026

CVSS v3.1
5.4
EPSS
0%
Percentile
14.0
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
5.4 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
CVSS v4.0
2.3 · 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
EPSS
0.00238 · 14.0th percentile
Weakness
CWE-862 · Missing Authorization
Published
2026-09-15T23:17Z
Affected products (1)
ProductVersionsFixed in
concretecms/concrete_cms≥ 8.5.3, < 9.5.39.5.3
References (1)
https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes · ff5b8ace-8b95-4078-9743-eac1ca5451de
EPSS history
Timeline
  • 17 SEP 03:32Z
    EPSS moved — → 0%
    epss
  • 15 SEP 18:48Z
    In Concrete CMS 8.5.3 to 9,5,2, OAuth 2.0 Refresh-Token Grant Bypasses Account Status
    cvelistv5