Mattermost up to 10.11.21/11.7.6/11.8.3 Board Member Validation BoardMember.Scheme privileges management

Summaryinfo

A vulnerability classified as critical has been found in Mattermost up to 10.11.21/11.7.6/11.8.3. This affects an unknown function of the component Board Member Validation. Performing a manipulation of the argument BoardMember.Scheme results in privileges management. This vulnerability is cataloged as CVE-2026-9816. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability classified as critical has been found in Mattermost up to 10.11.21/11.7.6/11.8.3. This affects some unknown processing of the component Board Member Validation. The manipulation of the argument BoardMember.Scheme with an unknown input leads to a privileges management vulnerability. CWE is classifying the issue as CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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

The advisory is shared at mattermost.com. This vulnerability is uniquely identified as CVE-2026-9816 since 05/28/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1068 for this issue.

Upgrading to version 10.11.22, 11.7.7, 11.8.4 or 11.9.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-60540). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Type

• Groupware Software

Name

• Mattermost

Version

• 10.11.0
• 10.11.1
• 10.11.2
• 10.11.3
• 10.11.4
• 10.11.5
• 10.11.6
• 10.11.7
• 10.11.8
• 10.11.9
• 10.11.10
• 10.11.11
• 10.11.12
• 10.11.13
• 10.11.14
• 10.11.15
• 10.11.16
• 10.11.17
• 10.11.18
• 10.11.19
• 10.11.20
• 10.11.21
• 11.7.0
• 11.7.1
• 11.7.2
• 11.7.3
• 11.7.4
• 11.7.5
• 11.7.6
• 11.8.0
• 11.8.1
• 11.8.2
• 11.8.3

License

• open-source

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CPE 2.2info

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If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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