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Mattermost DesktopApplication · Mattermost

CVE-2026-8683

MEDIUM · 6.5 CVSS v3.1 Published 2026-06-15
Fix available
A fix is available. Upgrade to after 6.1.5 or later.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable No privileges

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 Desktop App versions <=6.1 5.5.13.0 fail to account for attempting to open extremely long URLs in the Mattermost Desktop App which allows a malicious server owner to crash the application via including a script to call window.open on a very large URL. Mattermost Advisory ID: MMSA-2026-00652

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

The Mattermost Desktop App versions 6.1 and below and 5.5.13.0 fail to properly validate or limit URL length before attempting to open URLs via window.open. A malicious server owner can inject a script that calls window.open with an extremely long URL, causing the desktop application to crash due to the excessive resource consumption or failure to handle the oversized URL.

MitigationUpdate the Mattermost Desktop App to a version beyond 6.1 and 5.5.13.0 when a patched version becomes available, or implement URL length validation and error handling in the desktop client to prevent crashes from oversized URLs.

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 DesktopApplication
Affected:<= 5.13.0>= 6.1.0, <= 6.1.5

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
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

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 installed Mattermost Desktop version
    Open the Mattermost Desktop App, then navigate to the About section (typically found in the app menu under Help or About Mattermost) to view the exact version number
    Affected if The version displayed is either 5.13.0 or lower, or falls between 6.1.0 and 6.1.5 inclusive
  2. Confirm version is within affected ranges
    Compare the installed version number against the affected ranges: versions <= 5.13.0 or versions >= 6.1.0 through 6.1.5
    Affected if The installed version matches any of the affected version ranges listed in the CVE
  3. Verify URL handling is accessible
    Confirm the desktop application can load and connect to a Mattermost server, as the vulnerability triggers when the app attempts to open URLs via window.open from server-provided content
    Affected if The application can load and display content from a server, which enables the malformed URL to trigger the crash

A user is affected if they are running Mattermost Desktop version 5.13.0 or lower, or any version from 6.1.0 through 6.1.5, and the app can connect to a server that could attempt to exploit the URL handling.

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 a release after 6.1.5
Interim mitigation

Update the Mattermost Desktop App to a version beyond 6.1 and 5.5.13.0 when a patched version becomes available, or implement URL length validation and error handling in the desktop client to prevent crashes from oversized URLs.

Recommended fix Moderate confidence

Latest stable Mattermost Desktop App version (beyond 5.13.0 and 6.1.5)

  1. 1. Check the current Mattermost Desktop App version by navigating to Help > About Mattermost in the application menu
  2. 2. Download the latest stable version of Mattermost Desktop App from the official Mattermost download page (https://mattermost.com/download/)
  3. 3. Close the current Mattermost Desktop application completely
  4. 4. Install the downloaded latest version over the existing installation

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

Fix this in Mattermost Desktop Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,272.

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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-2026-8683 in production — separate from our analysis above.

No notes yet

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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