Vulnerability Details CVE-2026-18551
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
Exploit prediction scoring system (EPSS) score
EPSS Score 0.002
EPSS Ranking 12.8%
CVSS Severity
CVSS v3 Score 6.5
References
Products affected by CVE-2026-18551
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cpe:2.3:a:mattermost:mattermost_server:11.10.0
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cpe:2.3:a:mattermost:mattermost_server:11.7.0
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cpe:2.3:a:mattermost:mattermost_server:11.7.1
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cpe:2.3:a:mattermost:mattermost_server:11.7.2
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cpe:2.3:a:mattermost:mattermost_server:11.7.3
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cpe:2.3:a:mattermost:mattermost_server:11.7.4
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cpe:2.3:a:mattermost:mattermost_server:11.7.5
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cpe:2.3:a:mattermost:mattermost_server:11.7.6
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cpe:2.3:a:mattermost:mattermost_server:11.7.7
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cpe:2.3:a:mattermost:mattermost_server:11.7.8
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cpe:2.3:a:mattermost:mattermost_server:11.7.9
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cpe:2.3:a:mattermost:mattermost_server:11.8.0
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cpe:2.3:a:mattermost:mattermost_server:11.8.1
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cpe:2.3:a:mattermost:mattermost_server:11.8.2
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cpe:2.3:a:mattermost:mattermost_server:11.8.3
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cpe:2.3:a:mattermost:mattermost_server:11.8.4
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cpe:2.3:a:mattermost:mattermost_server:11.8.5
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cpe:2.3:a:mattermost:mattermost_server:11.9.0
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cpe:2.3:a:mattermost:mattermost_server:11.9.1