EUVD-2026-78202
GHSA-mfc3-273r-x6gf
Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:H/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
Registered user privilege (PR:L) more accurate than vendor PR:H; AC:H reflects non-default workflow configuration requirement; S:C for admin session hijack enabling privilege escalation; no direct availability impact.
Primary rating from Vendor (ff5b8ace-8b95-4078-9743-eac1ca5451de).
CVSS VectorVendor: ff5b8ace-8b95-4078-9743-eac1ca5451de
Lifecycle Timeline
3DescriptionCVE.org
Concrete CMS 8.3.0 to 9.5.2 stored calendar event names without sanitization and rendered them without HTML escaping in the workflow approval and deletion notifications shown in the dashboard "Waiting For Me" block. A registered user permitted to add events to a calendar governed by an approval workflow could submit an event whose name contained a script payload, which then executed in an administrator's browser when the pending request was displayed and could be used to create a new administrator account. 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:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks v01demort for reporting.
AnalysisAI
Stored XSS in Concrete CMS 8.3.0-9.5.2 permits a registered user with calendar event creation rights to inject script payloads via unsanitized event names that later execute in an administrator's browser through unescaped rendering in the dashboard "Waiting For Me" workflow notification block. Because the injected script runs under an active administrator session, an attacker can leverage it to silently create a new administrator account, achieving full CMS compromise. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Three concrete prerequisites must all be satisfied: (1) The target Concrete CMS installation must have at least one calendar configured with an approval workflow - this is a deliberate administrator-configured feature, not enabled in default out-of-box installations; (2) The attacker must possess a registered user account on the site with permission to add events to that workflow-governed calendar - a standard content-contributor role or equivalent; (3) An administrator must open the 'Waiting For Me' dashboard block to review the pending workflow approval or deletion notification containing the poisoned event name, which is routine behavior for admins managing content queues. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The real-world risk is moderate-to-high specifically for Concrete CMS installations using calendar approval workflows, but bounded by meaningful prerequisites. … 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 to Concrete CMS 9.5.3 or later, which resolves the vulnerability by applying proper HTML escaping to calendar event names before rendering them in workflow notification contexts. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, audit all Concrete CMS instances to identify which are running versions 8.3.0-9.5.2 and enumerate all users with calendar event creation permissions-these accounts are direct exploitation vectors. …
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External POC / Exploit Code
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