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Mattermost ServerApplication · Mattermost

CVE-2017-18900

CRITICAL · 9.8 CVSS v3.1 Published 2020-06-19
Fix available
A fix is available. Upgrade to 3.10.3 / 4.0.4 or later.
See remediation →
100/100
Remediation priority · Urgent
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 4.1.0, 4.0.4, and 3.10.3. It allows CSV injection via a compliance report.

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

CSV injection vulnerability in Mattermost Server's compliance reporting feature allows attackers to inject spreadsheet formula characters (such as =, +, -, @) into data fields that get executed when the exported CSV is opened in spreadsheet applications, potentially leading to code execution or data exfiltration.

MitigationUpgrade to Mattermost Server 4.1.0, 4.0.4, or 3.10.3 or later. As a temporary measure, restrict compliance reporting feature access to trusted administrators and sanitize or treat CSV files with caution before opening in spreadsheet applications.

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:< 3.10.3>= 4.0.0, < 4.0.4

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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. Determine installed Mattermost Server version
    Run 'mattermost version' from the command line, or check the version displayed in the System Console under About > Mattermost, or inspect the version file in the installation directory
    Affected if The installed version is less than 3.10.3, OR between 4.0.0 and 4.0.3 (inclusive)
  2. Verify compliance reporting is enabled
    Check the Mattermost config.json file for the 'ComplianceSettings' section, or navigate to Compliance > Configuration in the System Console
    Affected if The 'Enable' field in ComplianceSettings is set to true, or compliance reporting is shown as enabled in the UI
  3. Confirm compliance export functionality is accessible
    Navigate to Compliance > Reports in the System Console, or check if the API endpoint /api/v4/compliance/reports returns a valid response
    Affected if The compliance reporting interface is accessible and functional, allowing report creation or viewing
  4. Check user access to compliance exports
    Review System Console > Users to see which users have 'compliance' or 'admin' roles, or check the 'ComplianceExportDestination' setting in config.json
    Affected if There are users with compliance reporting access in the affected version

You are affected if running a vulnerable Mattermost Server version (pre-3.10.3 or 4.0.0-4.0.3) AND the compliance reporting feature is enabled and accessible.

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 3.10.3 / 4.0.4 or later
Fixed in 3.10.34.0.4
Interim mitigation

Upgrade to Mattermost Server 4.1.0, 4.0.4, or 3.10.3 or later. As a temporary measure, restrict compliance reporting feature access to trusted administrators and sanitize or treat CSV files with caution before opening in spreadsheet applications.

Recommended fix High confidence

4.1.0 or later (or 3.10.3+ for 3.x branch, 4.0.4+ for 4.0.x branch)

  1. 1. Identify current Mattermost Server version by checking the system console or running 'mattermost version'
  2. 2. If running version 3.x (< 3.10.3): Plan upgrade path to at least version 3.10.3, or preferably migrate to version 4.1.0 or later
  3. 3. If running version 4.0.0-4.0.3: Upgrade to version 4.0.4 minimum, or preferably version 4.1.0 or later
  4. 4. Before upgrading, backup the database and configuration files
  5. 5. Follow Mattermost upgrade documentation for your deployment type (team or enterprise)
  6. 6. After upgrade, verify the compliance reporting feature works correctly
  7. 7. Test that CSV export functionality in compliance reports functions as expected
Caveat Review Mattermost upgrade notes between your current version and target version for potential breaking changes, especially around database migrations

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

Fix this in Mattermost Server Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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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-2017-18900 in production — separate from our analysis above.

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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