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MEDIUM6.1

GO-2026-5360

Mattermost allows attackers to take over arbitrary user accounts via overly permissive substring matching flaw in github.com/mattermost/mattermost-server

Quick fix

GO-2026-5360 — github.com/mattermost/mattermost-server: upgrade to the fixed version with the command below.

go get github.com/mattermost/mattermost-server@v10.11.12+incompatible

Details

Mattermost allows attackers to take over arbitrary user accounts via overly permissive substring matching flaw in github.com/mattermost/mattermost-server

Are you affected?

Enter the version of the package you're using.

Affected packages

Go/github.com/mattermost/mattermost-server
Introduced in: 10.11.0-rc1+incompatibleFixed in: 10.11.12+incompatible
Fixgo get github.com/mattermost/mattermost-server@v10.11.12+incompatible
Go/github.com/mattermost/mattermost-server/v5
Introduced in: 0

No fixed version published yet for github.com/mattermost/mattermost-server/v5 (go modules). Pin to a known-safe version or switch to an alternative.

Go/github.com/mattermost/mattermost-server/v6
Introduced in: 0

No fixed version published yet for github.com/mattermost/mattermost-server/v6 (go modules). Pin to a known-safe version or switch to an alternative.

Go/github.com/mattermost/mattermost/server/v8
Introduced in: 8.0.0-20260105080200-d27a2195068dFixed in: 8.0.0-20260217110922-b7d4a1f1f59b
Fixgo get github.com/mattermost/mattermost/server/v8@v8.0.0-20260217110922-b7d4a1f1f59b

References