CVE-2026-8426 Concrete CMS does not validate a CSRF token before processing requests to `/dashboard/extend/update/prepare_remote_upgrade/<remoteMPID>`
An attacker can exploit a CSRF vulnerability in Concrete CMS to overwrite packages and execute arbitrary code if the victim has marketplace connectivity and package installation enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-8426?
CVE-2026-8426 is a high-severity vulnerability in Concretecms Concrete Cms, published on 21 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 does not validate a CSRF token before processing requests to /dashboard/extend/update/prepare_remote_upgrade/<remoteMPID>. An attacker who controls the remote package returned for a known marketplace item ID can overwrite the package PHP on disk and force its upgrade() method to execute in a single browser navigation. This results in remote code execution as the web server user. In order to be vulnerable, the victim must be passing canInstallPackages, victim site must be connected to the Concrete marketplace; and the attacker controls the package returned for a marketplace item ID already installed on the victim site. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 7.5 with vector CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks https://github.com/maru1009 for reporting.
Which versions are affected by CVE-2026-8426?
2 open source packages ship an affected version, including concrete5/concrete5. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
concrete5/concrete5 Packagist | All versions | 9.5.1 |
concrete5/concrete5 Packagist | All versions | 9.5.1 |
Products include Concretecms Concrete Cms.
How do I fix CVE-2026-8426?
Upgrade concrete5/concrete5 to 9.5.1 or later.
Is CVE-2026-8426 being exploited?
There is no known exploitation of CVE-2026-8426 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-5rj5-gfmr-hrc3.