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Mattermost ServerApplication · Mattermost

CVE-2017-18914

MEDIUM · 5.3 CVSS v3.1 Published 2020-06-19
Fix available
A fix is available. Upgrade to 3.6.7 / 3.7.5 or later.
See remediation →
62/100
Remediation priority · Elevated
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 3.8.2, 3.7.5, and 3.6.7. An external link can occur on an error page even if it is not on an allowlist.

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 confidence

This is an allowlist bypass vulnerability in Mattermost Server where external links can appear on error pages even when they are not configured on the allowlist. Error pages that should only display internal or approved links can be manipulated to show arbitrary external URLs, potentially enabling phishing or malicious redirects.

MitigationUpgrade Mattermost Server to version 3.8.2, 3.7.5, or 3.6.7 or later to resolve this allowlist bypass on error pages.

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:< 3.6.7>= 3.7.0, < 3.7.5>= 3.8.0, < 3.8.2

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
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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. Find Mattermost Server version
    Run the command: mmctl --version or check the system console under About > Mattermost or inspect the config.json file for the Version field
    Affected if The installed version matches < 3.6.7 OR >= 3.7.0 and < 3.7.5 OR >= 3.8.0 and < 3.8.2
  2. Verify SiteURL configuration
    Check the SiteURL setting in config.json or navigate to System Console > General > Configuration and verify the SiteURL value is set
    Affected if SiteURL is configured and the Server version is in the affected range listed above
  3. Check allowlist settings
    Navigate to System Console > Security > Policies or inspect the config.json for SiteStats or look for LinkPreviews or AllowedDomains settings
    Affected if Any allowlist or domain restrictions are configured AND the Server version is in the affected range

You are affected if your Mattermost Server version falls within the vulnerable ranges (< 3.6.7, 3.7.0-3.7.4, or 3.8.0-3.8.1) and you have a SiteURL configured, regardless of whether you have additional link restrictions in place.

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 3.6.7 / 3.7.5 / 3.8.2 or later
Fixed in 3.6.73.7.53.8.2
Interim mitigation

Upgrade Mattermost Server to version 3.8.2, 3.7.5, or 3.6.7 or later to resolve this allowlist bypass on error pages.

Fix this in Mattermost Server Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

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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-2017-18914 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