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CVE-2026-56290 – Unauthenticated File Upload Leading to RCE – Page Builder CK for Joomla (up to 3…

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Summary

CVE-2026-56290 is a critical unauthenticated arbitrary file upload vulnerability in the JoomlaCK.fr Page Builder CK extension for Joomla, affecting all versions up to and including 3.5.10. The flaw allows any unauthenticated remote attacker to upload executable files — including PHP web shells — directly to the server, resulting in full Remote Code Execution (RCE). With a CVSS 4.0 score of 10.0 and confirmed active exploitation in the wild, this vulnerability poses an immediate and severe risk to any Joomla site running the affected extension.

Technical details

  • Root cause: The extension’s front-end file upload handler performed no authentication or authorization checks. The only protection in place was a CSRF token, which any visitor could retrieve from the site’s own public pages in a single request.
  • Attack vector: Unauthenticated, network-accessible front-end endpoint; no privileges or user interaction required.
  • Trigger conditions: An attacker issues an HTTP POST request to the vulnerable upload endpoint, supplying a CSRF token obtained from the target site’s public pages — a trivial, single-step operation.
  • File control: The attacker controls both the destination directory and the uploaded filename, including the file extension. This allows placement of executable PHP files in any writable directory on the server, bypassing folder-level restrictions entirely.
  • Impact: Successful exploitation results in full Remote Code Execution on the underlying web server. Web shells (e.g., bhup.php) have been observed planted in the /media/com_pagebuilderck/gfonts/ directory on compromised sites, confirming active in-the-wild exploitation.

Affected software

  • JoomlaCK.fr Page Builder CK extension for Joomla: all versions up to and including 3.5.10
  • Legacy Joomla 3 builds: all Page Builder CK versions below 3.1.1
  • Legacy Joomla 4 builds: all Page Builder CK versions below 3.4.10

Severity

CVSS 4.0 Base Score: 10.0 (Critical)
Vector string: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:A/AU:Y/U:Red

Mitigation and recommended actions

  • Immediate action: Upgrade Page Builder CK to version 3.6.0, released June 27, 2026, which addresses this vulnerability by enforcing proper authentication and authorization on the file upload endpoint.
  • Joomla 3 legacy sites: Update to back-port release 3.1.1.
  • Joomla 4 legacy sites: Update to back-port release 3.4.10.
  • If immediate patching is not possible: Restrict external access to the vulnerable upload handler at the web server or WAF level until the update can be applied.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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Map your entire attack surface (continously)

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