Mattermost up to 11.10.x Member Roles API Endpoint privileges management

Summaryinfo

A vulnerability marked as critical has been reported in Mattermost up to 11.7.9/11.8.5/11.9.1/11.10.0/11.10.x. Impacted is an unknown function of the component Member Roles API Endpoint. Performing a manipulation results in privileges management. This vulnerability was named CVE-2026-18551. The attack may be initiated remotely. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical has been found in Mattermost up to 11.7.9/11.8.5/11.9.1/11.10.0/11.10.x. This affects an unknown code of the component Member Roles API Endpoint. The manipulation 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 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752

The advisory is shared at mattermost.com. This vulnerability is uniquely identified as CVE-2026-18551 since 08/01/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1068 for this issue.

Upgrading to version 11.7.10, 11.8.6, 11.9.2, 11.10.1 or 11.11.0 eliminates this vulnerability.

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Productinfo

Type

• Groupware Software

Name

• Mattermost

Version

• 11.0
• 11.1
• 11.2
• 11.3
• 11.4
• 11.5
• 11.6
• 11.7
• 11.7.0
• 11.7.1
• 11.7.2
• 11.7.3
• 11.7.4
• 11.7.5
• 11.7.6
• 11.7.7
• 11.7.8
• 11.7.9
• 11.8
• 11.8.0
• 11.8.1
• 11.8.2
• 11.8.3
• 11.8.4
• 11.8.5
• 11.9
• 11.9.0
• 11.9.1
• 11.10
• 11.10.0

License

• open-source

CPE 2.3info

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• 🔒
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CPE 2.2info

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• 🔒
• 🔒

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