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

Quick assessment

Affected
Concrete CMS Concrete CMS
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Concrete CMS 8.5.3 至 9.5.2 版本启用了基于未修改的 League OAuth 2.0 上游库的刷新令牌（refresh-token）授权方式。该实现允许在持有有效刷新令牌的情况下，直接签发新的访问令牌（access token），而不会重新检查关联账户的活跃状态。 因此，用户在账户处于活跃状态时获取的刷新令牌，在其账户被停用或挂起（即 uIsActive=0）后，仍可继续用于生成有效的访问令牌。这意味着即使停用某个用户账户，也无法撤销其对 API 的访问权限。 Concrete CMS 安

CVSS 2.3 · Low

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
Concrete CMS Concrete CMS 8.5.3≤ 9.5.2 affected
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I. Basic Information for CVE-2026-81921

Vulnerability Information
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Vulnerability Title
In Concrete CMS 8.5.3 to 9,5,2, OAuth 2.0 Refresh-Token Grant Bypasses Account Status
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制缺失
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Concrete CMS Concrete CMS 8.5.3 ~ 9.5.2 -

II. Public POCs for CVE-2026-81921

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III. Intelligence Information for CVE-2026-81921

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Vendor Pages for CVE-2026-81921 (1)

Same Patch Batch · Concrete CMS · 2026-09-15 · 31 CVEs total

CVE-2026-18110 8.7 HIGH Concrete CMS 9.0.0 through 9.5.2 is vulnerable to missing authorization in the user select
CVE-2026-81894 8.5 HIGH Concrete CMS 9.5.2 and below is vulnerable to Stored DOM-based Cross-site Scripting (XSS)
CVE-2026-18111 8.5 HIGH Concrete CMS below 9.5.4 allows privilege escalation because adding users and assigning gr
CVE-2026-81895 8.5 HIGH Concrete CMS 9.5.2 and below is vulnerable to Stored SQL Injection in Concrete CMS Documen
CVE-2026-81896 8.4 HIGH Concrete CMS below version 9.5.3 is vulnerable to Stored XSS in Concrete CMS Form Submissi
CVE-2026-81897 7.7 HIGH Concrete CMS below version 9.5.3 is vulnerable to Stored XSS via Express form Text control
CVE-2026-81898 7.5 HIGH Concrete CMS below version 9.5.3 is vulnerable to Stored XSS via country-less Address att
CVE-2026-18113 7.5 HIGH Concrete CMS 9.0 to 9.5.2 is vulnerable to Stored XSS in the Top Navigation Bar Block via
CVE-2026-18115 7.4 HIGH In Concrete CMS 9.2.0 to 9.5.2, Missing Authorization in REST API Users update() and chang
CVE-2026-81899 7.3 HIGH Concrete CMS 9.0 to 9.5.2 is vulnerable to Stored XSS via group folder name on the Members
CVE-2026-81919 2.3 LOW Concrete CMS below 9.5.3 is vulnerable to Cross-Site Request Forgery (CSRF) in Block Arran
CVE-2026-81920 2.3 LOW Concrete CMS below 9.5.3 is vulnerable to Cross-Site Request Forgery (CSRF) in Dashboard S
CVE-2026-68532 2.3 LOW Concrete CMS 9.0.0 to 9.5.2 is vunerable to CSRF in Concrete CMS Group Type Deletion Dashb
CVE-2026-68534 2.3 LOW Concrete CMS below 9.5.2 is vulnerable to Stored XSS via unescaped Express entry labels in
CVE-2026-68533 2.3 LOW Missing Authorization in Concrete CMS versions below 9.5.3 Conversation File Upload Allows
CVE-2026-81922 2.1 LOW "In Concrete CMS below 9.5.3, there is Missing authorization in the sitemap page reorder a
CVE-2026-81925 2.1 LOW Concrete CMS below 9.5.3 is vulnerable to Reflected Cross-Site Scripting (XSS) via Convers
CVE-2026-18424 2.1 LOW Concrete CMS 9.0.0 to 9.5.2 is vulnerable to SSRF protection bypass in remote file import
CVE-2026-18425 2.1 LOW IDOR in Concrete CMS 9.0.0 through 9.5.2 dashboard sitemap reorder (SitemapUpdate::updateD
CVE-2026-18422 2.1 LOW Concrete CMS below 9.5.3 Multilingual Page Assign Action Lacks Destination Authorization a

Showing top 20 of 31 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: Concrete CMS
Same vendor: Concrete CMS
Same weakness: CWE-862

V. Comments for CVE-2026-81921

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