Is github.com/mattermost/mattermost-server affected by CVE-2026-25783?

Go github.com/mattermost/mattermost-server is affected in >=10.11.0-rc1+incompatible =11.2.0-rc1+incompatible =11.3.0-rc1+incompatible <11.3.1+incompatible.

Is CVE-2026-25783 being exploited?

Not on the CISA KEV list. EPSS exploit probability is 0.3%.

medium

CVE-2026-25783

Q: Is CVE-2026-25783 being exploited?

Not on the CISA KEV list. EPSS exploit probability is 0.3%.

Go · github.com/mattermost/mattermost-server • Go · github.com/mattermost/mattermost-server/v5 • Go · github.com/mattermost/mattermost-server/v6 • Go · github.com/mattermost/mattermost/server/v8

Summary

Mattermost fails to properly validate User-Agent header tokens in github.com/mattermost/mattermost-server

Severity: medium
EPSS: 0.3% (p20)
Also known as: GHSA-2v3w-6g35-5f9v, GHSA-2v3w-6g35-5f9v#github.com/mattermost/mattermost-server, GHSA-2v3w-6g35-5f9v#github.com/mattermost/mattermost/server/v8, GO-2026-4725, GO-2026-4725#github.com/mattermost/mattermost-server, GO-2026-4725#github.com/mattermost/mattermost-server/v5, GO-2026-4725#github.com/mattermost/mattermost-server/v6, GO-2026-4725#github.com/mattermost/mattermost/server/v8
Published: 2026-03-26

References

Related advisories

CVE-2026-6346 — high · Go/github.com/mattermost/mattermost-server
CVE-2026-6347 — high · Go/github.com/mattermost/mattermost-server
CVE-2026-6339 — medium · Go/github.com/mattermost/mattermost-server
CVE-2026-5163 — medium · Go/github.com/mattermost/mattermost-server
CVE-2026-28732 — medium · Go/github.com/mattermost/mattermost-server
CVE-2026-6345 — medium · Go/github.com/mattermost/mattermost-server
CVE-2026-6340 — medium · Go/github.com/mattermost/mattermost-server
CVE-2026-3637 — medium · Go/github.com/mattermost/mattermost-server

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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.