EUVD-2026-75673
GHSA-xgrc-pc59-m8cp
Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:L/VI:H/VA:L/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
Attacker is authenticated with content-editor (Add Event) privileges, so PR:L; no scope change; confidentiality low, integrity high, availability low per description.
Primary rating from Vendor (ConcreteCMS).
CVSS VectorVendor: ConcreteCMS
Lifecycle Timeline
2DescriptionCVE.org
Concrete CMS versions 8.3.0 through 9.5.2 are vulnerable to an authorization bypass in the Calendar event edit dialog (concrete/controllers/dialog/event/edit.php). The dialog checked permissions against the calendar identifier supplied in the request rather than the calendar owning the targeted event occurrence. A user with the "Add Event" permission on a single calendar could read and overwrite events on calendars they were not permitted to access, and could delete an event's original local occurrence. Publishing the injected version to the live calendar, which demotes the previously approved version, additionally required the actor's approve_calendar_event workflow rights or an auto-approving workflow. The Concrete CMS Security Team gave this a rank of 5.9 with CVSS 4.0 vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N. Thanks Winston Crooker for reporting.
AnalysisAI
Calendar event authorization in Concrete CMS 8.3.0-9.5.2 is bypassed because the event edit dialog validates the actor's permissions against a calendar identifier supplied in the HTTP request rather than the calendar that actually owns the targeted event occurrence. An authenticated user holding 'Add Event' rights on any single calendar can read and overwrite events across all other calendars in the installation, and delete individual event occurrences; publishing the injected version as the live-approved revision additionally requires approve_calendar_event workflow rights or an auto-approving workflow. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The attacker must be an authenticated Concrete CMS user holding the 'Add Event' permission on at least one calendar within the installation (reflected by PR:H in the vendor's CVSS 4.0 vector, indicating a privileged non-anonymous role). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The Concrete CMS Security Team assigned CVSS 4.0 score 5.9 with PR:H and AT:P, reflecting that exploitation requires an authenticated content editor who already holds 'Add Event' permission on at least one calendar, and that the attacker must identify a reachable event on a restricted calendar - both genuine constraints that depress real-world risk relative to a raw integrity-high score. … 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 corrects the authorization check in the Calendar event edit dialog to validate the actor's permissions against the calendar that owns the targeted event rather than the caller-supplied calendar identifier; see the 9.5.3 release notes at https://documentation.concretecms.org/9-x/developers/introduction/version-history/953-release-notes. … Detailed patch versions, workarounds, and compensating controls in full report. |
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