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Mattermost ServerApplication · Mattermost

CVE-2026-9571

MEDIUM · 6.5 CVSS v3.1 Published 2026-07-13
Fix available
A fix is available. Upgrade to 10.11.20 / 11.6.5 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable Zero-click 5 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to invalidate OAuth refresh tokens upon user account deactivation, which allows a deactivated user or an attacker in possession of a valid refresh token to obtain new functional access tokens via the OAuth refresh token grant endpoint.. Mattermost Advisory ID: MMSA-2026-00680

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Mattermost fails to invalidate OAuth refresh tokens when user accounts are deactivated. Attackers with valid refresh tokens (from deactivated users or stolen tokens) can still obtain functional access tokens through the OAuth refresh token grant endpoint, bypassing account deactivation controls.

MitigationOrganizations should rotate all OAuth tokens immediately upon user deactivation and implement short token expiration policies. Upgrade to Mattermost versions 11.7.3+, 11.6.5+, or 10.11.20+ when released.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Mattermost ServerApplication
Affected:>= 10.11.0, < 10.11.20>= 11.6.0, < 11.6.5>= 11.7.0, < 11.7.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Mattermost Server version
    Run 'mattermost version' or check the server's /api/v4/system endpoint for the version field
    Affected if The version falls within 10.11.0-10.11.19, 11.6.0-11.6.4, or 11.7.0-11.7.2
  2. Confirm OAuth 2.0 applications are configured
    Check System Console > Integrations > OAuth 2.0 Applications, or query the database for active entries in the OAuthAccessTokens table
    Affected if OAuth 2.0 applications exist and users have been issued refresh tokens
  3. Verify user deactivation behavior for OAuth tokens
    Create a test user, configure an OAuth app, obtain a refresh token, deactivate the user, then attempt to use the refresh token to obtain a new access token
    Affected if The refresh token grant succeeds after user account deactivation, returning a valid access token

You are affected if your Mattermost Server version is in the vulnerable range and OAuth 2.0 applications are enabled, because deactivated user refresh tokens remain valid for obtaining access tokens.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 10.11.20 / 11.6.5 / 11.7.3 or later
Fixed in 10.11.2011.6.511.7.3
Interim mitigation

Organizations should rotate all OAuth tokens immediately upon user deactivation and implement short token expiration policies. Upgrade to Mattermost versions 11.7.3+, 11.6.5+, or 10.11.20+ when released.

Recommended fix High confidence

Upgrade to Mattermost Server 10.11.20, 11.6.5, or 11.7.3 (whichever is the latest in your current release branch)

  1. 1. Back up your Mattermost Server database and configuration files.
  2. 2. Download the appropriate Mattermost Server fixed release for your current version branch: 10.11.20 for 10.11.x, 11.6.5 for 11.6.x, or 11.7.3 for 11.7.x.
  3. 3. Stop the Mattermost Server service.
  4. 4. Upgrade Mattermost Server by following the official upgrade documentation for your installation method (e.g., tar.gz, Docker, or package manager).
  5. 5. Verify the upgrade completed successfully by checking the server version in the system console.
  6. 6. Test OAuth functionality to confirm refresh tokens are properly invalidated upon user deactivation.
  7. 7. Restart the Mattermost Server service.
Caveat Review Mattermost release notes for your target version for any breaking changes or required migration steps

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Mattermost Server Scoped from the published advisory
  • Consultation6.0 h
  • Implementation20.0 h
  • Testing10.0 h
  • Review / QA6.0 h
42.0 hours of engineering $7,380
Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-9571 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data