CVE-2026-9816Network attack vector

Board-admin escalation via unchecked Scheme flags

Published Aug 17, 2026 · Updated Aug 18, 2026

Privilege escalation in Mattermost Boards before 10.11.22, 11.7.7, and 11.8.4 allows remote authenticated users to grant Board Admin rights. In handleAddMember, the server honored caller-supplied BoardMember.Scheme* role flags on member-creation requests without restricting them to manage_board_roles users, and addUserToNewBoard copied archived SchemeAdmin values into imported members. A board editor or non-guest team member who can reach the add-member or archive-import paths can promote arbitrary users within a board; published records tie the flaw to Boards authorization and do not describe broader Mattermost system-role compromise.

CVSS severity8.3
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Privilege escalation in Mattermost Boards before 10.11.22, 11.7.7, and 11.8.4 allows remote authenticated users to grant Board Admin rights. In handleAddMember, the server honored caller-supplied BoardMember.Scheme* role flags on member-creation requests without restricting them to manage_board_roles users, and addUserToNewBoard copied archived SchemeAdmin values into imported members. A board editor or non-guest team member who can reach the add-member or archive-import paths can promote arbitrary users within a board; published records tie the flaw to Boards authorization and do not describe broader Mattermost system-role compromise.

The record

CVE
CVE-2026-9816
Published
Aug 17, 2026
Updated
Aug 18, 2026
Vendor
Mattermost
Product
Mattermost Boards
Classifications
CWE-863, T1098
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 17, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 18, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.11.0 <=10.11.21
  2. Affected versionversion=11.7.0 <=11.7.6
  3. Affected versionversion=11.8.0 <=11.8.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermost Boardsversion=10.11.0 <=10.11.21; version=11.7.0 <=11.7.6; version=11.8.0 <=11.8.3

Published CVSS scores

8.3MattermostCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-863Incorrect Authorization
T1098Account Manipulation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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