Is CVE-2026-8434 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-8434 being exploited in the wild.

How severe is CVE-2026-8434?

Medium severity, with a CVSS score of 4, published 21 May 2026.

Which products and versions are affected?

Concrete CMS 9.0.0 to 9.4.8; concrete5/concrete5 (Packagist) >= 9.0.0RC1, < 9.5.1, ECOSYSTEM:introduced=9.0.0RC1,fixed=9.5.1.

Is there a fix for CVE-2026-8434?

Yes. concrete5/concrete5 (Packagist): upgrade to 9.5.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-8434 attacked?

It is attacked over the network, in a network appliance.

Am I affected by CVE-2026-8434?

Check whether you run Concrete CMS or concrete5/concrete5 (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-8434: Concrete CMS CSRF in file rescanMultiple controller

Q: Is there a fix for CVE-2026-8434?

Yes. concrete5/concrete5 (Packagist): upgrade to 9.5.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-8434 attacked?

It is attacked over the network, in a network appliance.

Q: Am I affected by CVE-2026-8434?

Check whether you run Concrete CMS or concrete5/concrete5 (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-8434 · Severity: medium · CVSS 4 · Published 2026-05-21

Concrete CMS, a popular content management system, is vulnerable to a security flaw that could allow an attacker to trick an administrator into performing unintended file management actions. By convincing a logged-in user to click a malicious link, an attacker can trigger a 'rescan' of multiple files on the server. While this does not directly expose data, it allows unauthorized modification of system state and could disrupt administrative workflows.

Technologies: Concrete CMS, concrete5/concrete5 (Packagist). Vendors: Concrete CMS, Packagist.

Quick answers

Is CVE-2026-8434 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-8434 being exploited in the wild.
How severe is CVE-2026-8434?: Medium severity, with a CVSS score of 4, published 21 May 2026.
Which products and versions are affected?: Concrete CMS 9.0.0 to 9.4.8; concrete5/concrete5 (Packagist) >= 9.0.0RC1, < 9.5.1, ECOSYSTEM:introduced=9.0.0RC1,fixed=9.5.1.
Is there a fix for CVE-2026-8434?: Yes. concrete5/concrete5 (Packagist): upgrade to 9.5.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-8434 attacked?: It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-8434?: Check whether you run Concrete CMS or concrete5/concrete5 (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

concrete5/concrete5 (Packagist): upgrade to 9.5.1 or later
```
composer require concrete5/concrete5:^9.5.1
```

Technical details

A Cross-Site Request Forgery (CSRF) vulnerability exists in Concrete CMS versions 9.0.0RC1 through 9.5.0 within the 'concrete/controllers/backend/file' component. The 'rescanMultiple()' function fails to validate a security token (CSRF token) before processing requests. An attacker can exploit this by crafting a malicious webpage or link that, when visited by an authenticated administrator, silently submits a request to the vulnerable endpoint. This allows the attacker to force the application to rescan multiple files. The vulnerability is mitigated by the requirement for user interaction and the limited impact of the rescan action. The issue is addressed in version 9.5.1.

Affected products

Concrete CMS Concrete CMS >= 9.0.0RC1, < 9.5.1

Identifiers

CVE-2026-8434
GHSA-6qjh-p324-694f

Timeline

2026-05-21: disclosed: NVD Published Date
2026-05-22: advisory: GitHub Advisory published
2026-06-24: patched: GitHub Advisory reviewed and updated with patch info

References

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

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