CVE-2026-9816— Insufficient server-side validation of board member role fields permits privilege escalation
Quick assessment
Affected
Mattermost Mattermost
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
Mattermost是美国Mattermost公司开源的一个开源协作平台。 Mattermost 11.7.6及之前的11.7.x版本、10.11.21及之前的10.11.x版本和11.8.3及之前的11.8.x版本存在授权问题漏洞，该漏洞源于服务端在插入和归档导入路径中未能验证BoardMember.Scheme*字段，可能导致看板编辑者或非来宾团队成员通过POST /api/v2/boards/{boardID}/members和POST /api/v2/teams/{teamID}/archive/
Possible ATT&CK Techniques 1 AI
T1078 · Valid AccountsAffected Version Matrix 7
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Mattermost | Mattermost | 11.7.0≤ 11.7.6 |
affected |
10.11.0≤ 10.11.21 |
affected | ||
11.8.0≤ 11.8.3 |
affected | ||
11.9.0 |
unaffected | ||
11.7.7 |
unaffected | ||
10.11.22 |
unaffected | ||
11.8.4 |
unaffected |
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I. Basic Information for CVE-2026-9816
Vulnerability Information
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Vulnerability Title
Insufficient server-side validation of board member role fields permits privilege escalation
Source: CVE Program / CVE List V5
Vulnerability Description
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
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制不正确
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司开源的一个开源协作平台。 Mattermost 11.7.6及之前的11.7.x版本、10.11.21及之前的10.11.x版本和11.8.3及之前的11.8.x版本存在授权问题漏洞，该漏洞源于服务端在插入和归档导入路径中未能验证BoardMember.Scheme*字段，可能导致看板编辑者或非来宾团队成员通过POST /api/v2/boards/{boardID}/members和POST /api/v2/teams/{teamID}/archive/
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| Mattermost | Mattermost | 11.7.0 ~ 11.7.6 | - |
|
II. Public POCs for CVE-2026-9816
| # | POC Description | Source Link | Shenlong Link |
|---|
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Same Patch Batch · Mattermost · 2026-08-17 · 13 CVEs total
| CVE-2026-10080 | 6.5 MEDIUM | Boards plugin panics on WebSocket command with non-string field types |
| CVE-2026-9859 | 6.5 MEDIUM | Mattermost Boards plugin didn’t enforce role-based authorization on board channel link all |
| CVE-2026-16048 | 6.3 MEDIUM | Channel member roles accept out-of-scope roles |
| CVE-2026-10527 | 6.3 MEDIUM | Boards plugin retains Board Admin rights for users demoted to System Guest |
| CVE-2026-16047 | 4.3 MEDIUM | Board channel linking without read channel permission validation |
| CVE-2026-15754 | 4.2 MEDIUM | Missing per-channel team-scope check in ABAC access control policy unassign allows cross-t |
| CVE-2026-16049 | 3.9 LOW | _GitLab Plugin allows cross-channel post injection and phishing via missing channel permis |
| CVE-2026-16044 | 3.9 LOW | Insufficient validation of guest board admin privileges on archive import |
| CVE-2026-75587 | 3.6 LOW | Plaintext pre-auth secret exposure via Desktop App diagnostics report |
| CVE-2026-16046 | 3.5 LOW | Missing run-state validation on finished playbook runs |
| CVE-2026-9693 | 3.5 LOW | Mattermost thread memberships persist after team removal, exposing private channel thread |
| CVE-2026-16045 | 2.7 LOW | Delegated OAuth tokens could revoke unrelated OAuth application authorizations |
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