CVE-2026-85385: Concrete CMS below 9.5.4 is vulnerable to Stored XSS via User Timezone Field
Concrete CMS below 9.5.4 did not validate the user timezone value (uTimezone) on write and rendered it without output encoding on the Dashboard user management page, where Date::getTimezoneDisplayName() returns any non-IANA value unchanged. A stored cross-site scripting payload saved in this field executed in an administrator's browser when they viewed the affected user in the Dashboard, running script in the admin session (for example to read CSRF tokens, create administrator accounts, or change site settings). In Concrete CMS 9.5.3 the field became reachable by unauthenticated visitors through public registration; in Concrete CMS below 9.5.3, the same field was reachable by any authenticated user through the account profile editor. Exploitation required concrete.misc.usertimezones to be enabled (off by default), and the unauthenticated path additionally required public registration to be enabled. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 7.7 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks Suraj Bhosale for reporting.
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed by default?
The vulnerable timezone feature, concrete.misc.user_timezones, is disabled by default. A deployment is exposed only if this setting has been enabled.
Who can supply a malicious timezone value?
In version 9.5.3, unauthenticated visitors can reach the field through public registration when public registration is enabled. In versions below 9.5.3, any authenticated user can reach it through the account profile editor.
What user interaction is required for exploitation?
An administrator must view the affected user's record on the Dashboard user management page. The stored script then executes in that administrator's browser and session.
What can be done if an immediate upgrade is not possible?
Disable concrete.misc.user_timezones to prevent use of the vulnerable field. On 9.5.3, also disable public registration to remove the unauthenticated submission path.