CVE-2026-81905 Business logic in Concrete CMS
Attackers can redeem validation hashes for unintended purposes, enabling account takeover or activation if hashes are exposed via other channels.
- 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-2026-81905?
CVE-2026-81905 is a medium-severity 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 below 9.5.3 stores user validation hashes for multiple purposes (email/registration validation, password reset, and persistent login) in a single table with a type column, but the redemption path resolves a hash by value alone and does not verify its type. As a result, a hash issued for one purpose can be redeemed for another: a long-lived registration hash (60-day expiry) can be submitted to the password-change endpoint to set a new password on the target account, and a password-reset hash can be submitted to the email-validation endpoint to activate an account. Exploitation requires the attacker to first obtain a valid hash through a separate channel (for example email interception, log exposure, or SSRF against an internal mail relay), so the flaw amplifies the impact of any hash disclosure rather than creating a standalone entry point. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 6.3 with vector CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Yonatan Drori from Tenzai for reporting.
Which versions are affected by CVE-2026-81905?
How do I fix CVE-2026-81905?
No fix has been published for CVE-2026-81905 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-81905 being exploited?
There is no known exploitation of CVE-2026-81905 in the wild and no public exploit code.
Sources
Also known as GHSA-xgp3-243g-wxvm.