dbcve.org
MattermostApplication

CVE-2021-37860

MEDIUM · 6.1 CVSS v3.1 Published 2021-09-22
Fix available
A fix is available. Upgrade to after 5.38 or later.
See remediation →
68/100
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 5.38 and earlier fails to sufficiently sanitize clipboard contents, which allows a user-assisted attacker to inject arbitrary web script in product deployments that explicitly disable the default CSP.

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 versions 5.38 and earlier contain a cross-site scripting (XSS) vulnerability where clipboard contents are not properly sanitized before rendering. An attacker can inject malicious web scripts by tricking a user into copying crafted content to the clipboard, though this only impacts deployments where the default Content Security Policy has been explicitly disabled.

MitigationEnable or restore the default Content Security Policy (CSP) headers in the Mattermost configuration, which prevents XSS attacks regardless of input sanitization. If CSP cannot be enabled, apply the vendor patch that properly sanitizes clipboard content.

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
MattermostApplication
Affected:<= 5.38

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
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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. Check Mattermost server version
    Locate and inspect the Mattermost version from the system console, about page, or configuration files. Compare the installed version against the affected range (5.38 and earlier).
    Affected if The installed version is 5.38 or lower.
  2. Verify Content Security Policy configuration
    Examine the Mattermost configuration file (typically config.json) for the ContentSecurityPolicy setting. Determine whether CSP headers are enabled, disabled, or not defined.
    Affected if The ContentSecurityPolicy setting is explicitly disabled or removed from the configuration, making the deployment vulnerable regardless of version.

A user is affected if their Mattermost installation is version 5.38 or earlier AND the Content Security Policy has been explicitly disabled in the configuration.

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 a release after 5.38
Interim mitigation

Enable or restore the default Content Security Policy (CSP) headers in the Mattermost configuration, which prevents XSS attacks regardless of input sanitization. If CSP cannot be enabled, apply the vendor patch that properly sanitizes clipboard content.

Fix this in Mattermost Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-37860 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2021-37860 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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