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Medium, CVSS 5.3

Mattermost doesn't archive the channel before removing persistent notifications

CVE-2026-4635GHSA-pg7c-462j-grxv

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (github.com/mattermost/mattermost-server 11.6.1, 11.5.4, 11.4.5, 10.11.15), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

  • GitHub Advisory Database and maintainer security advisories on GitHub

    GitHub-reviewed advisory GHSA-pg7c-462j-grxv lists affected ranges: Go github.com/mattermost/mattermost-server >=11.6.0 =11.5.0 =11.4.0 =10.11.0 <10.11.15

    VerifiedObserved Structured GitHub Advisory Database record (type=reviewed) from the GitHub REST API.

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
5.3 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-4635: 0.17% estimated exploitation activity in the next 30 days; percentile 6.63 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to archive the channel before removing persistent notifications which allows authenticated user to crash the server via timing the creation of persistent notification message between the server deleting existing persistent notifications and archiving the channel. Mattermost Advisory ID: MMSA-2026-00637.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-pg7c-462j-grxv

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-4635

Advisory: Mattermost doesn't archive the channel before removing persistent notifications
IDs: CVE-2026-4635, GHSA-pg7c-462j-grxv
Record: https://patchnext.com/advisories/cve-2026-4635 (revision 1, source checked 26 Oct 2026, 15:24 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
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 11.6.1, 11.5.4, 11.4.5, 10.11.15. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/mattermost/mattermost-server: affected >= 11.6.0, <= 11.6.0; >= 11.5.0, < 11.5.4; >= 11.4.0, < 11.4.5; >= 10.11.0, < 10.11.15; fixed in 10.11.15, 11.4.5, 11.5.4, 11.6.1

## Suggested inspection (read-only)
- 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.
- 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-pg7c-462j-grxv (GitHub-reviewed advisory GHSA-pg7c-462j-grxv lists affected ranges: Go github.com/mattermost/mattermost-server >=11.6.0 =11.5.0 =11.4.0 =10.11.0 <10.11.15)

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