HIGH7.5
GO-2026-5838
Mattermost doesn't properly validate msgpack-encoded WebSocket frames before memory allocation in github.com/mattermost/mattermost-server
Quick fix
GO-2026-5838 — github.com/mattermost/mattermost-server: upgrade to the fixed version with the command below.
go get github.com/mattermost/mattermost-server@v10.11.15+incompatibleDetails
Mattermost doesn't properly validate msgpack-encoded WebSocket frames before memory allocation 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+incompatibleFixed in: 10.11.15+incompatibleFix
go get github.com/mattermost/mattermost-server@v10.11.15+incompatibleGo/github.com/mattermost/mattermost-server/v5
Introduced in:
0No 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:
0No 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:
0Fixed in: 8.0.0-20260410202636-17939826efa2Fix
go get github.com/mattermost/mattermost/server/v8@v8.0.0-20260410202636-17939826efa2