Vulnerability Description
Concrete CMS before 9.5.4 did not sanitize XML and XSLT documents uploaded through a public Form Block file-upload question. Plain XML uploads were validated by file extension only and stored as publicly accessible files that were served inline from the application's own origin. An unauthenticated visitor could therefore store an XML document containing an xml-stylesheet processing instruction that referenced an attacker-supplied, same-origin XSLT stylesheet. When a victim opened the stored file directly in a browser, the browser fetched the stylesheet, transformed the document into HTML, and executed attacker-controlled JavaScript in the Concrete CMS origin (stored cross-site scripting). If the victim was an authenticated administrator, the script could act with that administrator's session, and the reporter demonstrated creation of a new user in the Administrators group. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 7.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks Valentin SARRE (Independent security researcher) for reporting.
Related Weaknesses (CWE)
References
FAQ
What is CVE-2026-85386?
CVE-2026-85386 is a documented vulnerability. Concrete CMS before 9.5.4 did not sanitize XML and XSLT documents uploaded through a public Form Block file-upload question. Plain XML uploads were validated by file extension only and stored as publi...
How severe is CVE-2026-85386?
CVSS scoring is not yet available for CVE-2026-85386. Check NVD for updates.
Is there a patch for CVE-2026-85386?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.