CVE-2026-8821

HIGHPre-NVD 7.17.1—
EchelonGraph scoreHIGH confidence

Score 7.1 from GitHub Security Advisory (severity: HIGH) published 2026-09-14. a secondary CVSS source baseline 7.1; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this week
7.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.1Exploit: None knownExposed: 0

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

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field.. Mattermost Advisory ID: MMSA-2026-00677

CVSS v3
7.1
EG Score
7.1(high)
EG Risk
32(Track)
EG Risk 32/100SSVC: 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
Severity71% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
19%
KEV
Not listed

Published

September 14, 2026

Last Modified

September 16, 2026

Advisory Details (1)

Auto-updated Sep 14, 2026
No patch confirmed yet.
generic

Security Updates

https://mattermost.com/security-updates

Vendor Advisories for CVE-2026-8821(1)

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

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 27× in last 7d / 46× 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. 2026-09-25 09:46 UTCGHSA enrichment
  2. 2026-09-24 21:42 UTCEG score recompute
  3. 2026-09-24 21:42 UTCGHSA enrichment
  4. 2026-09-24 14:04 UTCEPSS rescore
  5. 2026-09-24 08:33 UTCGHSA enrichment
  6. 2026-09-23 20:29 UTCEG score recompute
  7. 2026-09-23 20:29 UTCGHSA enrichment
  8. 2026-09-23 17:54 UTCEPSS rescore
  9. 2026-09-23 08:26 UTCGHSA enrichment
  10. 2026-09-22 20:22 UTCEG score recompute
  11. 2026-09-22 20:22 UTCGHSA enrichment
  12. 2026-09-22 16:01 UTCEPSS rescore
  13. 2026-09-22 08:18 UTCEG score recompute
  14. 2026-09-22 08:18 UTCGHSA enrichment
  15. 2026-09-21 21:09 UTCEPSS rescore
  16. 2026-09-21 20:15 UTCGHSA enrichment
  17. 2026-09-21 08:11 UTCEG score recompute
  18. 2026-09-21 08:11 UTCGHSA enrichment
  19. 2026-09-20 20:16 UTCEPSS rescore
  20. 2026-09-20 20:07 UTCGHSA enrichment
  21. 2026-09-20 08:03 UTCGHSA enrichment
  22. 2026-09-19 19:59 UTCEG score recompute
  23. 2026-09-19 19:59 UTCGHSA enrichment
  24. 2026-09-19 07:55 UTCGHSA enrichment
  25. 2026-09-18 19:52 UTCEG score recompute
Show 21 more
  1. 2026-09-18 19:52 UTCGHSA enrichment
  2. 2026-09-18 19:28 UTCEPSS rescore
  3. 2026-09-18 07:48 UTCGHSA enrichment
  4. 2026-09-17 19:45 UTCEG score recompute
  5. 2026-09-17 19:45 UTCGHSA enrichment
  6. 2026-09-17 19:32 UTCEPSS rescore
  7. 2026-09-17 07:41 UTCGHSA enrichment
  8. 2026-09-16 19:36 UTCEG score recompute
  9. 2026-09-16 19:36 UTCGHSA enrichment
  10. 2026-09-16 14:09 UTCEPSS rescore
  11. 2026-09-16 12:44 UTCEG score recompute
  12. 2026-09-16 12:44 UTCGHSA enrichment
  13. 2026-09-16 05:15 UTCEPSS rescore
  14. 2026-09-16 00:40 UTCGHSA enrichment
  15. 2026-09-15 12:35 UTCGHSA enrichment
  16. 2026-09-15 00:30 UTCEG score recompute
  17. 2026-09-15 00:30 UTCGHSA enrichment
  18. 2026-09-14 12:26 UTCEG score recompute
  19. 2026-09-14 11:21 UTCEG score recompute
  20. 2026-09-14 10:45 UTCEG score recompute
  21. 2026-09-14 10:44 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-8821?
CVE-2026-8821 is a high vulnerability published on September 14, 2026. Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field..…
When was CVE-2026-8821 disclosed?
CVE-2026-8821 was first published in the National Vulnerability Database on September 14, 2026, with the most recent update on September 16, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-8821 actively exploited?
CVE-2026-8821 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 80.9% of all scored CVEs.
What is the CVSS score of CVE-2026-8821?
CVE-2026-8821 has a CVSS v3 base score of 7.1 (NVD).
How do I remediate CVE-2026-8821?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-8821, 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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