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Low, CVSS 3.8amended

Mattermost has an Incorrect Authorization issue

CVE-2026-8823GHSA-xmfh-3ccg-c9fx

What to do

Partial vendor fix. Follow the primary source's mitigation guidance and check back for a fix.

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

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

    Affected
    < 8.0.0-20260518160100-9bd77d3fc4d2
    Fixed in
    8.0.0-20260518160100-9bd77d3fc4d2

  • Go github.com/mattermost/mattermost-server/v6

    Affected
    every version
    Fixed in
    no fixed version recorded

  • Go github.com/mattermost/mattermost-server

    Affected
    >= 11.7.0, <= 11.7.0>= 10.11.0, < 10.11.18
    Fixed in
    11.7.1, 10.11.18

  • Go github.com/mattermost/mattermost-server/v5

    Affected
    every version
    Fixed in
    no fixed version recorded

Sources

  • Open Source Vulnerabilities (OSV.dev), including the GitHub Advisory Database

    OSV record GO-2026-6547 lists affected ranges: Go github.com/mattermost/mattermost-server >=10.11.0+incompatible =11.7.0+incompatible =0; Go github.com/mattermost/mattermost-server/v6 >=0; Go github.com/mattermost/mattermost/server/v8 >=0 <8.0.0-20260518160100-9bd77d3fc4d2 (fixed)

    VerifiedObserved Structured OSV record; not marked as GitHub-reviewed.

  • GitHub Advisory Database and maintainer security advisories on GitHub

    GitHub-reviewed advisory GHSA-xmfh-3ccg-c9fx lists affected ranges: Go github.com/mattermost/mattermost-server >=11.7.0 =10.11.0 =0 <8.0.0-20260518160100-9bd77d3fc4d2

    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
3.8 · CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L
EPSS
  • CVE-2026-8823: 0.32% estimated exploitation activity in the next 30 days; percentile 24.80 (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 11.7.x <= 11.7.0, 10.11.x <= 10.11.17 fail to validate bot targets when demoting users to guests which allows a lower-privileged administrator to degrade arbitrary bot accounts via the standard demote-user API.. Mattermost Advisory ID: MMSA-2026-00669

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-xmfh-3ccg-c9fx

  2. Revision 1 · created ·

    Published from osv record GO-2026-6547

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-2026-8823

Advisory: Mattermost has an Incorrect Authorization issue
IDs: CVE-2026-8823, GHSA-xmfh-3ccg-c9fx
Record: https://patchnext.com/advisories/cve-2026-8823 (revision 2, source checked 26 Oct 2026, 15:29 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/mattermost/mattermost/server/v8 8.0.0-20260518160100-9bd77d3fc4d2; github.com/mattermost/mattermost-server 11.7.1, 10.11.18. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/mattermost/mattermost/server/v8: affected < 8.0.0-20260518160100-9bd77d3fc4d2; fixed in 8.0.0-20260518160100-9bd77d3fc4d2
- Go github.com/mattermost/mattermost-server/v6: affected every version
- Go github.com/mattermost/mattermost-server: affected >= 11.7.0, <= 11.7.0; >= 10.11.0, < 10.11.18; fixed in 11.7.1, 10.11.18
- Go github.com/mattermost/mattermost-server/v5: affected every version

## 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/v6: check the installed version with your package manager.
- Go github.com/mattermost/mattermost-server: check the installed version with your package manager.
- Go github.com/mattermost/mattermost-server/v5: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## 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/v6, github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server/v5.
- 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://osv.dev/vulnerability/GO-2026-6547 (OSV record GO-2026-6547 lists affected ranges: Go github.com/mattermost/mattermost-server >=10.11.0+incompatible =11.7.0+incompatible =0; Go github.com/mattermost/mattermost-server/v6 >=0; Go github.com/mattermost/mattermost/server/v8 >=0 <8.0.0-20260518160100-9bd77d3fc4d2 (fixed))
- Verified: https://github.com/advisories/GHSA-xmfh-3ccg-c9fx (GitHub-reviewed advisory GHSA-xmfh-3ccg-c9fx lists affected ranges: Go github.com/mattermost/mattermost-server >=11.7.0 =10.11.0 =0 <8.0.0-20260518160100-9bd77d3fc4d2)

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