Vulnerability Details CVE-2026-18799
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 restrict Slack import account binding to system administrator-initiated imports which allows an authenticated attacker with team admin privileges to force-add existing Mattermost users to their team and forge posts attributed to those users' identities via a crafted Slack export containing target users' email addresses.. Mattermost Advisory ID: MMSA-2026-00757
Exploit prediction scoring system (EPSS) score
EPSS Score 0.002
EPSS Ranking 9.6%
CVSS Severity
CVSS v3 Score 4.3
References
Products affected by CVE-2026-18799
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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