CVE-2026-85385: concrete cms XSS (CVSS 9.6)

Description

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.user_timezones 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.

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CVSS v3.1 Score

9.6

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0050

Probability of exploitation

0.42%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-79 Cross-site Scripting (XSS)

Affected Products

Vendor	Product	Versions
concretecms	concrete_cms	< 9.5.4

References

Other References

https://documentation.concretecms.org/developers/introduction/version-history/954-release-notes

Frequently Asked Questions

What is CVE-2026-85385? +

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.user_timezones 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. It has a CVSS v3.1 base score of 9.6 (CRITICAL).

How severe is CVE-2026-85385? +

CVE-2026-85385 has a CVSS v3.1 score of 9.6 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0050, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-85385? +

CVE-2026-85385 affects products from concretecms, specifically: concrete_cms. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-85385? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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