CVE-2026-81925: Concrete CMS reflected XSS in conversation date format

CVE-2026-81925 · Severity: medium · CVSS 6.1 · Published 2026-09-15

Concrete CMS, a popular open-source content management system, contains a reflected cross-site scripting (XSS) vulnerability in its conversation messaging feature. An attacker can inject malicious JavaScript through a crafted date format parameter and trick a user into submitting it, allowing the attacker to steal session cookies, deface the page, or perform actions on behalf of the logged-in user. The vulnerability is particularly easy to exploit because the vulnerable endpoint lacks CSRF protection.

Technologies: Concrete CMS. Vendors: Concrete CMS.

Quick answers

Is CVE-2026-81925 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-81925 being exploited in the wild.
How severe is CVE-2026-81925?
Medium severity, with a CVSS score of 6.1, published 15 September 2026.
Which products and versions are affected?
Concrete CMS before 9.5.3.
Is there a fix for CVE-2026-81925?
A patch was published on 2026-09-15: Fixed in version 9.5.3 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-81925 attacked?
It is attacked over the network.
Am I affected by CVE-2026-81925?
Check whether you run Concrete CMS 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.

Technical details

The vulnerability is a reflected XSS flaw in Concrete CMS's conversation message rendering code. The root cause is improper neutralization (insufficient output encoding) of user-supplied custom date format strings when rendering conversation messages. An attacker can craft a malicious POST request containing JavaScript payload in the date format parameter and deliver it to a victim user. The attack requires the victim to be authenticated (PR:L) and to interact with a link or form submission (UI:P), but is aided by the absence of CSRF token validation on the endpoint, enabling cross-origin exploitation. The vulnerability affects versions before 9.5.3, and a patch is available in that version.

Affected products

  • Concrete CMS Concrete CMS before 9.5.3

Timeline

  • 2026-09-15: disclosed: CVE-2026-81925 published
  • 2026-09-15: patched: Fixed in version 9.5.3

References

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