EUVD-2026-80877
GHSA-2cmv-q7x4-7f79
Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
AC:H captures the stacked non-default config prerequisites, PR:N reflects the unauthenticated 9.5.3 path, UI:R for admin viewing, S:C for cross-context script, C:H/I:H for admin-session takeover, A:N as availability impact is only indirect.
Primary rating from Vendor (ConcreteCMS).
CVSS VectorVendor: ConcreteCMS
Lifecycle Timeline
2DescriptionCVE.org
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.
AnalysisAI
Stored cross-site scripting in Concrete CMS versions below 9.5.4 allows an attacker to persist a JavaScript payload in the user timezone field (uTimezone), which the Dashboard user-management page renders without output encoding so that the script runs inside an administrator's authenticated session - enabling theft of CSRF tokens, creation of rogue administrator accounts, or modification of site settings. Exploitation is conditionally gated rather than a broad drive-by threat: it requires the non-default setting concrete.misc.user_timezones to be enabled, and the unauthenticated write path exists only in 9.5.3 and only when public registration is also enabled, while versions below 9.5.3 permit only an authenticated user to write the field via the account profile editor; an administrator must subsequently view the malicious user record. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the non-default setting concrete.misc.user_timezones to be enabled (off by default). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | This is a genuine but conditionally-gated stored XSS (CWE-79) rather than a broad drive-by threat. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade Concrete CMS to 9.5.4 or later, which is the vendor-released patch documented in the 9.5.4 release notes at https://documentation.concretecms.org/developers/introduction/version-history/954-release-notes. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, verify whether the non-default setting concrete.misc.user_timezones is enabled on all Concrete CMS instances; if it is not required, disable it immediately, and also disable public user registration if not essential, as these are prerequisites for exploitation in certain versions. …
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External POC / Exploit Code
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