Is github.com/mattermost/mattermost/server/v8 affected by CVE-2026-28759?

Go github.com/mattermost/mattermost/server/v8 is affected in >=11.5.0 =10.11.0 =11.4.0 <11.4.4, <8.0.0-20260216150504-8738f8c4b3d4.

Is CVE-2026-28759 being exploited?

Not on the CISA KEV list. EPSS exploit probability is 0.2%.

medium

CVE-2026-28759

Q: Is CVE-2026-28759 being exploited?

Not on the CISA KEV list. EPSS exploit probability is 0.2%.

Go · github.com/mattermost/mattermost/server/v8 • Go · github.com/mattermost/mattermost-server

Summary

Mattermost does not verify remote cluster channel access when processing shared channel membership removals

Severity: medium
EPSS: 0.2% (p5)
Also known as: GHSA-8h9w-w78c-vvr3#github.com/mattermost/mattermost-server, GHSA-8h9w-w78c-vvr3#github.com/mattermost/mattermost/server/v8
Published: 2026-05-18

References

Related advisories

CVE-2026-6346 — high · Go/github.com/mattermost/mattermost/server/v8
CVE-2026-3108 — high · Go/github.com/mattermost/mattermost/server/v8
CVE-2026-6339 — medium · Go/github.com/mattermost/mattermost/server/v8
CVE-2026-6343 — medium · Go/github.com/mattermost/mattermost/server/v8
CVE-2026-5163 — medium · Go/github.com/mattermost/mattermost/server/v8
CVE-2026-28732 — medium · Go/github.com/mattermost/mattermost/server/v8
CVE-2026-6345 — medium · Go/github.com/mattermost/mattermost/server/v8
CVE-2026-6340 — medium · Go/github.com/mattermost/mattermost/server/v8

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Sources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.