CVE-2026-81906 [UNREVIEWED] OAuth Callback Login Bypasses Deactivated-Account Checks
Attackers can bypass deactivated or unvalidated account checks during OAuth login to establish authenticated sessions in Concrete CMS.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-81906?
CVE-2026-81906 is a medium-severity authentication bypass vulnerability in Concrete CMS, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-288
Which versions are affected by CVE-2026-81906?
How do I fix CVE-2026-81906?
No fix has been published for CVE-2026-81906 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-2026-81906 being exploited?
There is no known exploitation of CVE-2026-81906 in the wild and no public exploit code.
Sources
Also known as GHSA-2c5v-fhhf-mwq5.