Is CVE-2026-8340 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-8340 being exploited in the wild.

How severe is CVE-2026-8340?

Medium severity, with a CVSS score of 4.3, published 22 May 2026.

Which products and versions are affected?

Concrete CMS <= 9.5.0, 9.5.0 and below; concrete5/concrete5 (Packagist) < 9.5.1, ECOSYSTEM:introduced=0,fixed=9.5.1.

Is there a fix for CVE-2026-8340?

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-2026-8340 attacked?

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

Am I affected by CVE-2026-8340?

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-2026-8340: Concrete CMS CSRF in Backend File Version Approval

Q: Which products and versions are affected?

Concrete CMS <= 9.5.0, 9.5.0 and below; concrete5/concrete5 (Packagist) < 9.5.1, ECOSYSTEM:introduced=0,fixed=9.5.1.

Q: Is there a fix for CVE-2026-8340?

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-2026-8340 attacked?

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

Q: Am I affected by CVE-2026-8340?

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-2026-8340 · Severity: medium · CVSS 4.3 · Published 2026-05-22

Concrete CMS, a platform used for building and managing websites, is vulnerable to a security flaw that could allow an attacker to trick a site editor into performing unintended actions. By deceiving a user with file editing permissions, an attacker can force the system to publish an older version of a file or activate an unpublished version created by another user. This could lead to the unauthorized replacement of current website content with outdated or unvetted information.

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

Quick answers

Is CVE-2026-8340 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-8340 being exploited in the wild.
How severe is CVE-2026-8340?: Medium severity, with a CVSS score of 4.3, published 22 May 2026.
Which products and versions are affected?: Concrete CMS <= 9.5.0, 9.5.0 and below; concrete5/concrete5 (Packagist) < 9.5.1, ECOSYSTEM:introduced=0,fixed=9.5.1.
Is there a fix for CVE-2026-8340?: 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-2026-8340 attacked?: It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-8340?: 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 9.5.0 and earlier within the 'Backend\File::approveVersion' method. The application fails to properly validate CSRF tokens when a user with 'edit_file_contents' permissions approves a file version. An attacker can exploit this by inducing a logged-in editor to visit a malicious site, which then triggers a background request to the CMS. This results in the publication of an attacker-selected file version, such as a downgrade to a previous version or the activation of a co-editor's unpublished draft. The vulnerability is addressed in version 9.5.1.

Affected products

Concrete CMS Concrete CMS <= 9.5.0

Identifiers

CVE-2026-8340
GHSA-xjg6-5v39-v7fc

Timeline

2026-05-22: disclosed: NVD published date
2026-05-26: advisory: GitHub Advisory published
2026-06-29: patched: GitHub Advisory reviewed and updated with patch information

References

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

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