CVE-2021-37863
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 · uneditedMattermost 6.0 and earlier fails to sufficiently validate parameters during post creation, which allows authenticated attackers to cause a client-side crash of the web application via a maliciously crafted post.
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 · moderate confidenceMattermost 6.0 and earlier lacks sufficient server-side validation of post creation parameters, allowing authenticated users to submit maliciously crafted posts that cause a client-side crash in the web application. This is a client-side denial-of-service vulnerability stemming from improper input validation.
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<= 6.0CVSS 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
- Required
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/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 checksWork through these to decide whether this CVE applies to you.
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Determine Mattermost Server versionRun 'grep -i version /opt/mattermost/version.go' or access the Mattermost system console and navigate to About > Mattermost, or use the API endpoint /api/v4/system/versionAffected if The installed version is 6.0 or earlier (any 6.0.x or prior release)
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Verify web client is accessibleAccess the Mattermost web interface URL and confirm the login page loads successfullyAffected if The web client is accessible and the server is running a vulnerable version
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Confirm user authentication is enabledCheck Mattermost configuration file (config.json) for 'EnableSignUpWithEmail' or 'EnableSignInWithEmail' set to true, or verify that LDAP/SAML/OAuth authentication methods are configured and activeAffected if User authentication is enabled, allowing authenticated users to create posts
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Verify post creation is permittedCheck that the Mattermost server is not in read-only mode and that public channels exist where authenticated users can post messagesAffected if Authenticated users have the ability to create posts in any channel
If Mattermost Server version is 6.0 or earlier and authenticated users can post to channels, the environment is vulnerable to client-side crashes via malicious post payloads.
Generated from the published advisory. Verify against your own configuration.
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 · scopedUpgrade to the patched Mattermost version that implements proper parameter validation on post creation. Implement server-side input sanitization and validation to reject malformed post data before processing and broadcasting to clients.
Mattermost Server 6.1 or later
- 1. Back up your Mattermost server data and configuration
- 2. Ensure you have a recent database backup
- 3. Review Mattermost upgrade documentation for your deployment type
- 4. Upgrade Mattermost Server to version 6.1 or later
- 5. Verify the upgrade was successful by checking the server logs
- 6. Test post creation functionality to confirm the vulnerability is remediated
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,408.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-37863 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-37863 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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