CVE-2026-9816

HIGHPre-NVD 8.38.3—
EchelonGraph scoreHIGH confidence

Score 8.3 from GitHub Security Advisory (severity: HIGH) published 2026-08-18. a secondary CVSS source baseline 8.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 4 sources updated this week
8.3EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 8.3Exploit: None knownExposed: 0

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

Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate BoardMember.Scheme* fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST /api/v2/boards/{boardID}/members and POST /api/v2/teams/{teamID}/archive/import.. Mattermost Advisory ID: MMSA-2026-00685

CVSS v3
8.3
EG Score
8.3(high)
EG Risk
37(Track)
EG Risk 37/100SSVC: 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
Severity83% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
16%
KEV
Not listed

Published

August 17, 2026

Last Modified

August 19, 2026

Advisory Details (1)

Auto-updated Aug 17, 2026
No patch confirmed yet.
generic

Security Updates

https://mattermost.com/security-updates

Vendor Advisories for CVE-2026-9816(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 21× in last 7d / 21× 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. 2026-08-21 00:37 UTCEG score recompute
  2. 2026-08-21 00:37 UTCGHSA enrichment
  3. 2026-08-20 22:56 UTCEPSS rescore
  4. 2026-08-20 13:04 UTCGHSA enrichment
  5. 2026-08-20 01:17 UTCEG score recompute
  6. 2026-08-20 01:17 UTCGHSA enrichment
  7. 2026-08-19 17:04 UTCEPSS rescore
  8. 2026-08-19 13:43 UTCGHSA enrichment
  9. 2026-08-19 04:16 UTCGHSA enrichment
  10. 2026-08-18 16:43 UTCEG score recompute
  11. 2026-08-18 16:43 UTCGHSA enrichment
  12. 2026-08-18 15:32 UTCEG score recompute
  13. 2026-08-18 15:32 UTCGHSA enrichment
  14. 2026-08-18 15:23 UTCEG score recompute
  15. 2026-08-18 15:23 UTCGHSA enrichment
  16. 2026-08-18 13:49 UTCEPSS rescore
  17. 2026-08-18 09:54 UTCEG score recompute
  18. 2026-08-18 09:54 UTCGHSA enrichment
  19. 2026-08-17 22:21 UTCEG score recompute
  20. 2026-08-17 22:09 UTCEG score recompute
  21. 2026-08-17 22:08 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-9816?
CVE-2026-9816 is a high vulnerability published on August 17, 2026. Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate BoardMember.Scheme* fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST…
When was CVE-2026-9816 disclosed?
CVE-2026-9816 was first published in the National Vulnerability Database on August 17, 2026, with the most recent update on August 19, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-9816 actively exploited?
CVE-2026-9816 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 83.9% of all scored CVEs.
What is the CVSS score of CVE-2026-9816?
CVE-2026-9816 has a CVSS v3 base score of 8.3 (NVD).
How do I remediate CVE-2026-9816?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-9816, 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

Explore the affected products and dependency analysis for CVE-2026-9816

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