CVE-2026-8426

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.

CVSS v3.1 Score

8.8

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0017

Probability of exploitation

0.07%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-352 Cross-Site Request Forgery

CWE-829 CWE-829

Affected Products

Vendor	Product	Versions
concretecms	concrete_cms	< 9.5.1

References

Other References

https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes

Frequently Asked Questions

What is CVE-2026-8426? +

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. It has a CVSS v3.1 base score of 8.8 (HIGH).

How severe is CVE-2026-8426? +

CVE-2026-8426 has a CVSS v3.1 score of 8.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0017, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-8426? +

CVE-2026-8426 affects products from concretecms, specifically: concrete_cms. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-8426? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-40325

Masa CMS is a content management system forked from Mura CMS. In versions 7.5.2 and earlier, the `cTrash.restore` function does …

CVE-2026-40174

Masa CMS is a content management system forked from Mura CMS. In versions 7.5.2 and earlier, the cUsers.updateAddress function does …

CVE-2024-6662

Websites managed by MegaBIP in versions below 5.15 are vulnerable to Cross-Site Request Forgery (CSRF) as the form available under …

CVE-2026-42286

Emlog is an open source website building system. Prior to version 2.6.11, missing CSRF protection in critical admin functions allows …

CVE-2026-9591

Cross-site request forgery (CSRF) in NewsItemApiController in SimplCommerce prior to commit 6233d73e allows an unauthenticated remote attacker to create or …

CVE-2024-7141

Versions of Gliffy Online prior to versions 4.14.0-7 contains a Cross Site Request Forgery (CSRF) flaw.