CVE-2026-8426
Analyzed Analyzed - Analysis Complete
Remote Code Execution in Concrete CMS

Publication date: 2026-05-21

Last updated on: 2026-05-26

Assigner: ConcreteCMS

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.
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Meta Information
Published
2026-05-21
Last Modified
2026-05-26
Generated
2026-06-11
AI Q&A
2026-05-22
EPSS Evaluated
2026-06-10
NVD
CVE-2026-8426
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
concretecms concrete_cms to 9.5.1 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-352 The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.
CWE-829 The product imports, requires, or includes executable functionality (such as a library) from a source that is outside of the intended control sphere.
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Executive Summary

This vulnerability affects Concrete CMS version 9.5.0 and below, where the system does not validate a CSRF token before processing requests to a specific URL related to remote package upgrades.

An attacker who controls the remote package returned for a known marketplace item ID can overwrite the package PHP file on disk and force its upgrade() method to execute with a single browser navigation.

This leads to remote code execution with the permissions of the web server user.

To be vulnerable, the victim site must have the ability to install packages, be connected to the Concrete marketplace, and the attacker must control the package returned for an already installed marketplace item ID.

Impact Analysis

This vulnerability can allow an attacker to execute arbitrary code remotely on the affected server with the privileges of the web server user.

Such remote code execution can lead to full compromise of the affected system, including unauthorized access, data theft, data modification, or further attacks within the network.

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