CVE-2026-81903: Concrete CMS 9.0.0 to 9.5.2 is vulnerable to Stored XSS via Page Container icon
Concrete CMS versions 9.0.0 to 9.5.2 stored the Page Container icon value submitted through the dashboard without validating it against the set of known container icons. The unvalidated value was later concatenated into the src attribute of an img tag by a helper that did not encode attribute output, and was rendered raw in the Containers dashboard list and editor views. A user with delegated access to the Page Containers dashboard could store a crafted icon value that broke out of the src attribute and executed script in the authenticated session of another editor or administrator who viewed the list, enabling session token theft and privileged dashboard actions. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 7.0 with vector CVSS:4.0/AV:A/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks Andrew Gonzalez for reporting.
Affected Software
Event History
Frequently Asked Questions
Who can exploit this issue, and who is at risk from the stored payload?
Exploitation requires a user with delegated access to the Page Containers dashboard to submit a crafted icon value. Editors or administrators are at risk when they view the Containers dashboard list or editor views containing the stored value.
What could an attacker do after successful exploitation?
The crafted value can execute script in the authenticated viewer's session. The described impacts include theft of session tokens and performing privileged dashboard actions as the affected editor or administrator.
Which versions are affected?
Concrete CMS versions 9.0.0 through 9.5.2 are affected.