CVE-2026-6046
Mattermost doesn't validate that a username returned during bot registration belongs to a bot account
Summary
Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username. Mattermost Advisory ID: MMSA-2026-00649
Affected packages
| Ecosystem | Package | Affected versions | Fixed versions |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | — | 11.6.1, 11.5.5, 10.11.17 |
| Go | github.com/mattermost/mattermost/server/v8 | — | 8.0.0-20260428151657-c79c3831061a |
Remediation: Upgrade to 11.6.1 or later.
References
Includes data from the GitHub Advisory Database, licensed under CC-BY 4.0.
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EPSS scores provided by the FIRST.org Exploit Prediction Scoring System.