CVE-2026-81906
MEDIUMDescription
Concrete CMS OAuth callback login path prior to version 9.5.3 did not check whether an account was active or email-validated before establishing a session. A deactivated or unvalidated user with an existing OAuth binding could complete authentication and receive a session that was fully authenticated for the callback response, with the login recorded and login events dispatched. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 6.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Yonatan Drori from Tenzai for reporting.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v4 Vector
Exploitability
Impact
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/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
Exploit Intelligence
Low risk: more likely to be exploited than 32% of all known CVEs.
References
Related Vulnerabilities
Other CWE-288 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2024-1709 | Critical | 10.0 | 100% | KEV + Ransom | Fix |
| CVE-2023-42793 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2024-27198 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2025-4427 | Medium | 5.3 | 100% | KEV | Fix |
| CVE-2024-55591 | Critical | 9.8 | 98% | KEV + Ransom | Fix |
| CVE-2023-46747 | Critical | 9.8 | 97% | KEV + Ransom | - |
Common questions
How do I fix CVE-2026-81906?
No published fix for CVE-2026-81906 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-81906 being actively exploited?
Not that we know of. CVE-2026-81906 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.39% is the estimated probability that it will be exploited in the next 30 days. That is higher than 32% of all scored CVEs.
How severe is CVE-2026-81906?
CVE-2026-81906 has a CVSS v4 base score of 6.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-11.