CVE-2026-8340 Concrete CMS 9.5.0 and below is vulnerable to CSRF via Backend\File::approveVersion

What is CVE-2026-8340?

CVE-2026-8340 is a low-severity vulnerability in Concretecms Concrete Cms, published on 22 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

Concrete CMS 9.5.0 and below is vulnerable to CSRF via Backend\File::approveVersion. Victim with edit_file_contents permission is CSRF'd into publishing an attacker-chosen previously-uploaded version (downgrade to an older version of a file, or activation of a co-editor's unpublished version). The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 2.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Winston Crooker for reporting.

Weakness: CWE-352

Which versions are affected by CVE-2026-8340?

2 open source packages ship an affected version, including concrete5/concrete5. It affects 1 product.

Products include Concretecms Concrete Cms.

How do I fix CVE-2026-8340?

Upgrade concrete5/concrete5 to 9.5.1 or later.

Is CVE-2026-8340 being exploited?

There is no known exploitation of CVE-2026-8340 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 Critical 9.8
• CVE-2022-21829 Code injection in concrete CMS Critical 9.8
• CVE-2021-22958 Server-Side Request Forgery vulnerability in concrete5 Critical 9.8
• CVE-2021-40098 Path traversal in n/a Critical 9.8
• CVE-2026-8134 Concrete CMS Vulnerable to Relative Path Traversal Critical 9.4

All Concretecms Concrete Cms vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-xjg6-5v39-v7fc.