Vulnerability-Lookup

GHSA-CWC3-87MF-4GGW

Vulnerability from github – Published: 2026-09-11 00:31 – Updated: 2026-09-11 00:31

Details

Concrete CMS 9.5.2 and below is vulnerable to an authorization bypass (IDOR) because the frontend calendar lightbox endpoint (/ccm/calendar/view_event/{bID}/{occurrence_id}) does not verify that the caller is permitted to view the calendar that owns the requested event occurrence. The controller loads the occurrence directly from an attacker‑supplied, sequential identifier without confirming that it belongs to the calendar configured on the referenced block. An unauthenticated visitor who can render any public calendar block with lightbox properties enabled could therefore supply an arbitrary occurrence identifier and disclose event metadata — title, date, description, page link, and configured event attributes — from calendars they are not permitted to view. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 6.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks riodrwn for reporting.

Severity

6.3 (Medium)


                  
                    CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

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{
  "affected": [],
  "aliases": [
    "CVE-2026-18121"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-639"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-11T00:17:28Z",
    "severity": "MODERATE"
  },
  "details": "Concrete CMS 9.5.2 and below is vulnerable to an authorization bypass (IDOR) because the frontend calendar lightbox endpoint (/ccm/calendar/view_event/{bID}/{occurrence_id}) does not verify that the caller is permitted to view the calendar that owns the requested event occurrence. The controller loads the occurrence directly from an attacker\u2011supplied, sequential identifier without confirming that it belongs to the calendar configured on the referenced block. An unauthenticated visitor who can render any public calendar block with lightbox properties enabled could therefore supply an arbitrary occurrence identifier and disclose event metadata \u2014 title, date, description, page link, and configured event attributes \u2014 from calendars they are not permitted to view. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 6.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks riodrwn for reporting.",
  "id": "GHSA-cwc3-87mf-4ggw",
  "modified": "2026-09-11T00:31:16Z",
  "published": "2026-09-11T00:31:16Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-18121"
    },
    {
      "type": "WEB",
      "url": "https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/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",
      "type": "CVSS_V4"
    }
  ]
}

CVE-2026-18121 (GCVE-0-2026-18121)

Vulnerability from cvelistv5 – Published: 2026-09-10 23:10 – Updated: 2026-09-11 14:33

Title

Concrete CMS 9.5.2 and below is vulnerable to an authorization bypass (IDOR) in the Calendar block's frontend event dialog (/ccm/calendar/view_event/{bID}/{occurrence_id}).

Summary

Severity

6.3 (Medium)


                        
                          CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-11 14:32 UTC

CWE

CWE-862 - Missing Authorization
CWE-639 - Authorization bypass through User-Controlled key

Assigner

ConcreteCMS mitre root

References

1 reference

URL	Tags
https://documentation.concretecms.org/developers/…	release-notes

Impacted products

1 product

Vendor	Product	Version
Concrete CMS	Concrete CMS	Affected: 5.0.0 , ≤ 9.5.2 (git)

Credits

riodrwn

Show details on NVD website

JSON

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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

GHSA-CWC3-87MF-4GGW

CVE-2026-18121 (GCVE-0-2026-18121)

Tags

Sightings

Nomenclature