Mattermost doesn't enforce slash command trigger-word uniqueness during command updates

Exploitation

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

CVSS

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

EPSS

• CVE-2026-28732: 0.15% estimated exploitation activity in the next 30 days; percentile 4.40 (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 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 Fail to enforce slash command trigger-word uniqueness during command updates which allows an authenticated team member with Manage Own Slash Commands permission to hijack and impersonate existing system or custom slash commands via editing their own slash command trigger to an already-registered trigger through the command update API. Mattermost Advisory ID: MMSA-2026-00597

Published by the source

18 May 2026, 09:31 UTC

Last modified by the source

1 Jun 2026, 15:13 UTC

Source last checked

26 Oct 2026, 15:23 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-wvcv-9xpm-7mqc

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# Patch Next advisory brief: CVE-2026-28732

Advisory: Mattermost doesn't enforce slash command trigger-word uniqueness during command updates
IDs: CVE-2026-28732, GHSA-wvcv-9xpm-7mqc
Record: https://patchnext.com/advisories/cve-2026-28732 (revision 1, source checked 26 Oct 2026, 15:23 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
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/server/v8 11.5.2, 11.4.4, 10.11.14, 8.0.0-20260306123948-f5fe8ded6b63; github.com/mattermost/mattermost-server 5.3.2-0.20260306123948-f5fe8ded6b63. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/mattermost/mattermost/server/v8: affected >= 11.5.0, < 11.5.2; >= 10.11.0, < 10.11.14; >= 11.4.0, < 11.4.4; < 8.0.0-20260306123948-f5fe8ded6b63; fixed in 11.4.4, 10.11.14, 11.5.2, 8.0.0-20260306123948-f5fe8ded6b63
- Go github.com/mattermost/mattermost-server: affected < 5.3.2-0.20260306123948-f5fe8ded6b63; fixed in 5.3.2-0.20260306123948-f5fe8ded6b63

## Suggested inspection (read-only)
- Go github.com/mattermost/mattermost/server/v8: check the installed version with your package manager.
- Go github.com/mattermost/mattermost-server: 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/server/v8, github.com/mattermost/mattermost-server.
- 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-wvcv-9xpm-7mqc (GitHub-reviewed advisory GHSA-wvcv-9xpm-7mqc lists affected ranges: Go github.com/mattermost/mattermost/server/v8 >=11.5.0 =10.11.0 =11.4.0 =0 =0 <5.3.2-0.20260306123948-f5fe8ded6b63)

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