Is CVE-2026-8203 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-8203 being exploited in the wild.

How severe is CVE-2026-8203?

High severity, with a CVSS score of 4, published 21 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-2026-8203?

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-2026-8203 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-8203?

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-2026-8203: Concrete CMS Stored XSS in height parameter

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-2026-8203?

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-2026-8203 attacked?

It is attacked over the network, in a web application.

Q: Am I affected by CVE-2026-8203?

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-2026-8203 · Severity: high · CVSS 4 · Published 2026-05-21

Concrete CMS, a popular content management system, is vulnerable to a security flaw where malicious code can be stored within the system. An attacker with editor-level privileges can inject scripts that execute in the browsers of other users or visitors. This could allow an attacker to steal login sessions, capture sensitive user information, or perform unauthorized actions on behalf of other users.

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

Quick answers

Is CVE-2026-8203 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-8203 being exploited in the wild.
How severe is CVE-2026-8203?: High severity, with a CVSS score of 4, published 21 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-2026-8203?: 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-2026-8203 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-8203?: 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 Stored Cross-Site Scripting (XSS) vulnerability exists in Concrete CMS versions 9.5.0 and earlier. The vulnerability is located in the controller responsible for handling the 'height' parameter, which fails to properly validate or sanitize input. An authenticated attacker with editor privileges can submit a malicious payload that is stored on the server. When other users, including administrators or site visitors, view the affected content, the malicious JavaScript executes in their browser context. This can lead to session hijacking (via cookie theft) or credential harvesting. The issue is addressed in version 9.5.1.

Affected products

Concrete CMS Concrete CMS <= 9.5.0

Identifiers

CVE-2026-8203
GHSA-9v2g-37mp-qpxf

Timeline

2026-05-21: disclosed
2026-05-21: advisory
2026-05-21: patched: Fixed in version 9.5.1

References

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

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