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Mattermost ServerApplication · Mattermost

CVE-2020-14447

HIGH · 7.5 CVSS v3.1 Published 2020-06-19
Fix available
A fix is available. Upgrade to 5.23.0 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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
An issue was discovered in Mattermost Server before 5.23.0. Large webhook requests allow attackers to cause a denial of service (infinite loop), aka MMSA-2020-0021.

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 Server before 5.23.0 contains a denial of service vulnerability where processing large webhook requests triggers an infinite loop, causing the service to become unresponsive. Attackers can exploit this by sending specially crafted large webhook payloads.

MitigationUpgrade Mattermost Server to version 5.23.0 or later. As an interim measure, implement rate limiting on webhook endpoints and monitor for abnormal request patterns.

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:< 5.23.0

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
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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. Check installed Mattermost Server version
    Run 'mattermost version' or check the System Console under About > Mattermost, or inspect the version file in the installation directory
    Affected if Version is lower than 5.23.0
  2. Verify incoming webhooks are enabled
    Navigate to System Console > Integrations > Integration Management, or check config.json for 'EnableIncomingWebhooks' setting set to true
    Affected if Incoming webhooks are enabled and the server version is below 5.23.0
  3. Verify outgoing webhooks are enabled
    Navigate to System Console > Integrations > Integration Management, or check config.json for 'EnableOutgoingWebhooks' setting set to true
    Affected if Outgoing webhooks are enabled and the server version is below 5.23.0
  4. Confirm webhook endpoints are network-accessible
    Review firewall rules and network configuration to determine if webhook endpoints (typically /api/v4/webhooks) are reachable from untrusted networks
    Affected if Webhook endpoints are externally accessible and the server version is below 5.23.0

The environment is affected if Mattermost Server version is below 5.23.0 and webhook integrations are enabled and reachable.

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.

From vendor data
Upgrade available Upgrade to 5.23.0 or later
Fixed in 5.23.0
Interim mitigation

Upgrade Mattermost Server to version 5.23.0 or later. As an interim measure, implement rate limiting on webhook endpoints and monitor for abnormal request patterns.

Fix this in Mattermost Server Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
16.0 hours of engineering $2,760
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,416.

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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-2020-14447 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