CVE-2026-18121

MEDIUMPre-NVD 6.36.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 78% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Trending — 3 sources updated this week
6.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.3Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
6.3
EG Score
6.3(medium)
EG Risk
28(Track)
EG Risk 28/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity63% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
22%
KEV
Not listed

Published

September 10, 2026

Last Modified

September 11, 2026

References (1)

Vendor Advisories for CVE-2026-18121(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 19× in last 7d / 33× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-20 22:32 UTCEG score recompute
  2. 2026-09-20 22:32 UTCGHSA enrichment
  3. 2026-09-20 00:14 UTCEG score recompute
  4. 2026-09-20 00:14 UTCGHSA enrichment
  5. 2026-09-19 01:56 UTCEG score recompute
  6. 2026-09-19 01:56 UTCGHSA enrichment
  7. 2026-09-18 19:27 UTCEPSS rescore
  8. 2026-09-18 03:38 UTCEG score recompute
  9. 2026-09-18 03:38 UTCGHSA enrichment
  10. 2026-09-17 05:20 UTCEG score recompute
  11. 2026-09-17 05:20 UTCGHSA enrichment
  12. 2026-09-16 14:07 UTCEPSS rescore
  13. 2026-09-16 07:02 UTCEG score recompute
  14. 2026-09-16 07:01 UTCGHSA enrichment
  15. 2026-09-16 05:14 UTCEPSS rescore
  16. 2026-09-15 08:44 UTCEG score recompute
  17. 2026-09-15 08:44 UTCGHSA enrichment
  18. 2026-09-14 10:24 UTCEG score recompute
  19. 2026-09-14 10:24 UTCGHSA enrichment
  20. 2026-09-13 16:46 UTCEPSS rescore
  21. 2026-09-13 12:06 UTCEG score recompute
  22. 2026-09-13 12:06 UTCGHSA enrichment
  23. 2026-09-12 15:00 UTCEPSS rescore
  24. 2026-09-12 13:48 UTCGHSA enrichment
  25. 2026-09-11 15:29 UTCGHSA enrichment
Show 8 more
  1. 2026-09-11 14:53 UTCEG score recompute
  2. 2026-09-11 14:53 UTCGHSA enrichment
  3. 2026-09-11 14:52 UTCEPSS rescore
  4. 2026-09-11 14:44 UTCEG score recompute
  5. 2026-09-11 14:44 UTCGHSA enrichment
  6. 2026-09-11 00:19 UTCEG score recompute
  7. 2026-09-10 23:21 UTCEG score recompute
  8. 2026-09-10 23:20 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-18121?
CVE-2026-18121 is a medium vulnerability published on September 10, 2026. Concrete CMS 9.5.2 and below is vulnerable to an authorization bypass (IDOR) because the frontend calendar lightbox endpoint (/ccm/calendar/viewevent/{bID}/{occurrenceid}) does not verify that the caller is permitted to view the calendar that owns the requested event occurrence. The controller…
When was CVE-2026-18121 disclosed?
CVE-2026-18121 was first published in the National Vulnerability Database on September 10, 2026, with the most recent update on September 11, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-18121 actively exploited?
CVE-2026-18121 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 78.3% of all scored CVEs.
What is the CVSS score of CVE-2026-18121?
CVE-2026-18121 has a CVSS v3 base score of 6.3 (NVD).
How do I remediate CVE-2026-18121?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-18121, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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