CVE-2026-87031 Missing authorization in Concrete CMS
Attackers with valid OAuth tokens can create arbitrary user accounts bypassing verification, leading to privilege escalation and potential content modification.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-87031?
CVE-2026-87031 is a low-severity missing authorization vulnerability in Concretecms Concrete Cms, published on 16 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official description
n Concrete CMS 9.2.0 through 9.5.3, the REST API user creation endpoint (POST /ccm/api/1.0/users, the add() method of concrete/src/Api/Controller/Users.php) did not perform a permission check before creating an account. As a result, any valid OAuth token carrying the users:add scope, including a client_credentials token with no associated user context, could create active, validated user accounts, bypassing email verification and administrator approval. Under default registration settings the created accounts could then edit page content, providing a path to stored cross-site scripting and further compromise. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 2.1 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Winston Crooker for reporting.
Weakness: CWE-862
Which versions are affected by CVE-2026-87031?
It affects 1 product.
Products include Concretecms Concrete Cms.
How do I fix CVE-2026-87031?
No fix has been published for CVE-2026-87031 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-87031 being exploited?
There is no known exploitation of CVE-2026-87031 in the wild and no public exploit code.
Other vulnerabilities in Concretecms Concrete Cms
- CVE-2023-48648 Concrete CMS allows unauthorized access because directories can be created with insecure permissions
- CVE-2022-21829 Code injection in concrete CMS
- CVE-2021-22958 Server-Side Request Forgery vulnerability in concrete5
- CVE-2021-40098 Path traversal in n/a
- CVE-2026-8134 Concrete CMS Vulnerable to Relative Path Traversal
Sources
Also known as GHSA-82fx-23wg-996j.