Mattermost fails to check Websocket request for proper UTF-8 format potentially crashing Calls plug-in

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2025-12689: 0.29% estimated exploitation activity in the next 30 days; percentile 21.39 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Mattermost versions 11.0.x <= 11.0.4, 10.12.x <= 10.12.2, 10.11.x <= 10.11.6 fail to check WebSocket request field for proper UTF-8 format, which allows attacker to crash Calls plug-in via sending malformed request.

Published by the source

17 Dec 2025, 21:30 UTC

Last modified by the source

20 Dec 2025, 17:13 UTC

Source last checked

26 Oct 2026, 15:13 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-j5vq-62gr-8v3r

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# Patch Next advisory brief: CVE-2025-12689

Advisory: Mattermost fails to check Websocket request for proper UTF-8 format potentially crashing Calls plug-in
IDs: CVE-2025-12689, GHSA-j5vq-62gr-8v3r
Record: https://patchnext.com/advisories/cve-2025-12689 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/mattermost/mattermost-plugin-calls 1.11.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/mattermost/mattermost-plugin-calls: affected < 1.11.0; fixed in 1.11.0

## Suggested inspection (read-only)
- Go github.com/mattermost/mattermost-plugin-calls: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/mattermost/mattermost-plugin-calls.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-j5vq-62gr-8v3r (GitHub-reviewed advisory GHSA-j5vq-62gr-8v3r lists affected ranges: Go github.com/mattermost/mattermost-plugin-calls >=0 <1.11.0)

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