CVE-2026-9816

HIGHPre-NVD 8.38.3
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

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, GitHub Security Advisory, a secondary CVSS source
Trending — 3 sources updated this week
8.3EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.4%CVSS: 8.3Exploit: None knownExposed services: Not assessed

Update Mattermost to versions 11.9.0, 11.7.7, 10.11.22, 11.8.4 or higher (from the CVE record's solution, Mattermost, Inc.) — apply it.

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
8.3HIGHmedium confidence
EG Risk
37
EG Risk 37/100

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 (value × EchelonGraph’s weight)
Severity83% × 45%
The EG Score, 8.3 of 10.
Exploitation0.4% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: Update Mattermost to versions 11.9.0, 11.7.7, 10.11.22, 11.8.4 or higher (from the CVE record's solution, Mattermost, Inc.). Apply it within your standard update timelines.
EPSS PROB
0.4%
EPSS %ILE
26th
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

Update Mattermost to versions 11.9.0, 11.7.7, 10.11.22, 11.8.4 or higher (from the CVE record's solution, Mattermost, Inc.). Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

August 17, 2026

Last Modified

August 19, 2026

Advisory Details (1)

Auto-updated Aug 17, 2026
Fix named in the CVE record's solution (Mattermost, Inc.).
Web page

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 15× in last 7d / 99× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 100 of 201 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 101 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-11 19:10 UTCEG score recompute
  2. 2026-10-11 16:25 UTCEG score recompute
  3. 2026-10-11 13:50 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  4. 2026-10-11 13:37 UTCEG score recompute
  5. 2026-10-10 20:01 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  6. 2026-10-09 20:08 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  7. 2026-10-08 17:14 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  8. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  9. 2026-10-07 11:24 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  10. 2026-10-06 21:43 UTCEG score recompute
  11. 2026-10-06 21:43 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  12. 2026-10-06 15:19 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  13. 2026-10-06 09:00 UTCEG score recompute
  14. 2026-10-06 09:00 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  15. 2026-10-05 17:44 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  16. 2026-10-05 09:38 UTCEG score recompute
  17. 2026-10-05 09:38 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  18. 2026-10-04 23:23 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  19. 2026-10-04 21:47 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  20. 2026-10-04 05:20 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  21. 2026-10-03 17:45 UTCEG score recompute
  22. 2026-10-03 17:45 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  23. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  24. 2026-10-03 03:17 UTCEG score recompute
  25. 2026-10-03 03:17 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
Show 75 more
  1. 2026-10-02 17:57 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  2. 2026-10-02 15:43 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  3. 2026-10-02 01:33 UTCEG score recompute
  4. 2026-10-02 01:33 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  5. 2026-10-01 19:51 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  6. 2026-10-01 09:12 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  7. 2026-09-30 21:38 UTCEG score recompute
  8. 2026-09-30 21:38 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  9. 2026-09-30 15:04 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  10. 2026-09-30 09:56 UTCEG score recompute
  11. 2026-09-30 09:56 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  12. 2026-09-29 15:24 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  13. 2026-09-28 21:58 UTCEG score recompute
  14. 2026-09-28 21:58 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  15. 2026-09-28 13:52 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  16. 2026-09-28 07:10 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  17. 2026-09-27 19:36 UTCEG score recompute
  18. 2026-09-27 19:36 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  19. 2026-09-27 13:49 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  20. 2026-09-27 08:03 UTCEG score recompute
  21. 2026-09-27 08:03 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  22. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.4% · 26th percentile
  23. 2026-09-25 01:51 UTCEG score recompute
  24. 2026-09-25 01:51 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  25. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.4% · 25th percentile
  26. 2026-09-24 08:00 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  27. 2026-09-23 20:26 UTCEG score recompute
  28. 2026-09-23 20:26 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  29. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  30. 2026-09-23 08:12 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  31. 2026-09-22 20:37 UTCEG score recompute
  32. 2026-09-22 20:37 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  33. 2026-09-22 16:01 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  34. 2026-09-22 08:42 UTCEG score recompute
  35. 2026-09-22 08:42 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  36. 2026-09-21 21:09 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  37. 2026-09-21 21:08 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  38. 2026-09-21 09:34 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  39. 2026-09-20 22:01 UTCEG score recompute
  40. 2026-09-20 22:01 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  41. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  42. 2026-09-20 10:26 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  43. 2026-09-19 22:52 UTCEG score recompute
  44. 2026-09-19 22:52 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  45. 2026-09-19 10:58 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  46. 2026-09-18 23:23 UTCEG score recompute
  47. 2026-09-18 23:23 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  48. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  49. 2026-09-18 11:50 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  50. 2026-09-18 00:17 UTCEG score recompute
  51. 2026-09-18 00:17 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  52. 2026-09-17 19:32 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  53. 2026-09-17 11:04 UTCEG score recompute
  54. 2026-09-17 11:04 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  55. 2026-09-16 23:15 UTCEG score recompute
  56. 2026-09-16 23:15 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  57. 2026-09-16 14:09 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  58. 2026-09-16 11:41 UTCEG score recompute
  59. 2026-09-16 11:41 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  60. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  61. 2026-09-16 00:01 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  62. 2026-09-15 11:42 UTCEG score recompute
  63. 2026-09-15 11:42 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  64. 2026-09-15 03:12 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  65. 2026-09-14 22:31 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  66. 2026-09-14 10:58 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  67. 2026-09-13 23:24 UTCEG score recompute
  68. 2026-09-13 23:24 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  69. 2026-09-13 16:48 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  70. 2026-09-13 11:51 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  71. 2026-09-13 00:17 UTCEG score recompute
  72. 2026-09-13 00:17 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  73. 2026-09-12 15:02 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  74. 2026-09-12 12:43 UTCGHSA enrichmentGHSA-h2c9-x337-f543 · GitHub severity HIGH · GitHub CVSS 8.3
  75. 2026-09-12 01:09 UTCEG score recompute

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-9816?
CVE-2026-9816 is a high-severity vulnerability; its CVE record was 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 the CVE record for CVE-2026-9816 published?
The CVE record for CVE-2026-9816 was published on August 17, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of August 19, 2026; the record at its source may have been updated since.
Is CVE-2026-9816 actively exploited?
CVE-2026-9816 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.4% probability of exploitation in the next 30 days (26th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-9816?
CVE-2026-9816 has a CVSS base score of 8.3 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-9816?
The CVE record's solution for CVE-2026-9816, written by its CNA Mattermost, Inc., names the fix: "Update Mattermost to versions 11.9.0, 11.7.7, 10.11.22, 11.8.4 or higher." The vendor advisories EchelonGraph has for CVE-2026-9816 are linked in the Vendor Advisories panel on this page.

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