CVE-2026-27769: Mattermost doesn't validate whether users were correctly owned by the correct Connected Workspace

April 17, 2026 (updated April 28, 2026)

Mattermost versions 10.11.x <= 10.11.12 fail to validate whether users were correctly owned by the correct Connected Workspace which allows a malicious remote server connected using the Conntexted Workspaces feature to change the displayed status of local users via the Connected Workspaces API. Mattermost Advisory ID: MMSA-2026-00603.

References

github.com/advisories/GHSA-mxxh-fmjq-j6x4
github.com/mattermost/mattermost
mattermost.com/security-updates
nvd.nist.gov/vuln/detail/CVE-2026-27769

Code Behaviors & Features

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