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GHSA-3vmp-whvv-5v9v

Mattermost doesn't validate that a username returned during bot registration belongs to a bot account

Source: GitHub Advisory Database (reviewed) Moderate CVE-2026-6046

Packages

EcosystemPackageAffectedFixed in
Go github.com/mattermost/mattermost-server >= 11.6.0, < 11.6.1 11.6.1
Go github.com/mattermost/mattermost-server >= 11.5.0, < 11.5.5 11.5.5
Go github.com/mattermost/mattermost-server >= 10.11.0, < 10.11.17 10.11.17
Go github.com/mattermost/mattermost/server/v8 >= 8.0.0-20250731163400-5b955468ea1e, < 8.0.0-20260428151657-c79c3831061a 8.0.0-20260428151657-c79c3831061a

Details

As written in the advisory (Markdown source, shown as plain text).

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

References

External links from the advisory. They lead to third-party sites.