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CVE-2026-81921

🔶 medium
🔍 Scan for this CVE
Summary

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 vulnerabil

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.

CVSS Score
5.4
Medium
EPSS Score
0.1
Exploit Probability
Published Date
2026-09-15
First Seen: 2026-09-17
📊 Relative Risk Intelligence

This CVE is Lower Risk - more severe than 22.2% of all 360,548 vulnerabilities in our database.

#280,402
Below average severity
Severity Percentile
🎯 CISA SSVC Assessment Updated: Sep 15, 2026
🔍 Exploitation Status
None
No known exploits
⚙️ Automatable
NO
Requires human interaction
💥 Technical Impact
Partial
Limited system impact
🏆 Discovered By
sh4d0byss
SSVC data provided by CISA
Last Modified 2026-09-18
Source NVD 🔗
CVSS Vector 3.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
CVSS Vector 4.0 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CWE IDs (Weakness Types)
CWE-862

📦 Affected Products 1

Vendor Product Status Affected Versions
concretecms concrete_cms Affected
> 8.5.3 < 9.5.3

🔗 References 1

https://documentation.concretecms.org/developers/int...
Broken Link

🔗 Related CVEs 6

CVE ID Severity CVSS EPSS Summary Published
CVE-2026-81894 🔶 medium 5.4 0.1 Concrete CMS 9.5.2 and below is vulnerable to stored DOM-based Cross-site Scripting (XSS) via the Gallery block's per-im... 2026-09-15
CVE-2026-81895 ⚠️ high 7.2 0.3 In Concrete CMS before 9.5.3, the Document Library block stored the file-set identifiers submitted through fsID[] withou... 2026-09-15
CVE-2026-81896 🔶 medium 5.4 0.1 Concrete CMS before 9.5.3 does not apply HTML entity encoding to user-defined Form block question labels when rendering ... 2026-09-15
CVE-2026-81897 🔶 medium 5.4 0.1 In Concrete CMS below CMS 9.5.3, the save_control action in the Express entities forms dashboard controller did not vali... 2026-09-15
CVE-2026-81919 🔶 medium 4.3 0.1 Concrete CMS below 9.5.3 did not validate an anti-CSRF token on the block-arrangement backend endpoint (the arrange() ac... 2026-09-15
CVE-2026-81920 🔶 medium 4.3 0.1 Concrete CMS below 9.5.3 was vulnerable to Cross-Site Request Forgery in the dashboard SEO Excluded Words page. The rese... 2026-09-15
These CVEs affect the same products