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MattermostApplication

CVE-2024-39274

MEDIUM · 6.5 CVSS v3.1 Published 2024-08-01
Fix available
A fix is available. Upgrade to 9.5.7 / 9.7.6 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable 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
Mattermost versions 9.9.x <= 9.9.0, 9.5.x <= 9.5.6, 9.7.x <= 9.7.5 and 9.8.x <= 9.8.1 fail to properly validate that the channel that comes from the sync message is a shared channel, when shared channels are enabled, which allows a malicious remote to add users to arbitrary teams and channels

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

In Mattermost's shared channels feature, the server fails to properly validate that incoming sync messages originate from a legitimate shared channel when shared channels are enabled. This allows a malicious remote Mattermost server to send crafted sync messages that trick the vulnerable server into adding users to arbitrary teams and channels, bypassing intended access controls.

MitigationUpgrade to the patched versions (9.9.1, 9.5.7, 9.7.6, 9.8.2 or later) or disable shared channels if not required. If upgrading is not immediately possible, review audit logs for unexpected team/channel membership changes and consider network-level controls to restrict sync message sources.

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:>= 9.5.0, < 9.5.7>= 9.7.0, < 9.7.6>= 9.8.0, < 9.8.2= 9.9.0

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/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 installed Mattermost version
    Run 'mmctl version' or check the About section in the Mattermost System Console to retrieve the exact server version number
    Affected if Version falls within any of these ranges: 9.5.0-9.5.6, 9.7.0-9.7.5, 9.8.0-9.8.1, or 9.9.0
  2. Verify shared channels feature status
    Navigate to System Console > Shared Channels, or query the database table 'PluginState' or check the 'SharedChannels' setting in config.json
    Affected if Shared channels are enabled and the server version is in an affected range
  3. Inspect audit logs for unauthorized membership changes
    Search System Console > Audit Logs for events such as 'add_user_to_team', 'add_user_to_channel' with unexpected timestamps or source IPs, or query the audit_logs table filtering for 'team_id' and 'channel_id' changes from non-local users
    Affected if Audit logs show team or channel membership additions that were not initiated by local administrators
  4. Review connected remote servers in shared channels
    Navigate to System Console > Shared Channels > Remote Clusters, or query the 'RemoteClusters' table in the database to list all configured remote Mattermost servers
    Affected if Unexpected or unauthorized remote server entries exist in the shared channel configuration

A server is affected if it runs a version in the vulnerable ranges (9.5.0-9.5.6, 9.7.0-9.7.5, 9.8.0-9.8.1, or 9.9.0) AND has shared channels feature enabled, regardless of whether exploitation is observed in audit logs.

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 9.5.7 / 9.7.6 / 9.8.2 or later
Fixed in 9.5.79.7.69.8.2
Interim mitigation

Upgrade to the patched versions (9.9.1, 9.5.7, 9.7.6, 9.8.2 or later) or disable shared channels if not required. If upgrading is not immediately possible, review audit logs for unexpected team/channel membership changes and consider network-level controls to restrict sync message sources.

Recommended fix High confidence

Upgrade to 9.5.7 (if on 9.5.x), 9.7.6 (if on 9.7.x), 9.8.2 (if on 9.8.x), or 9.9.1+ (if on 9.9.x)

  1. 1. Identify your current Mattermost version by checking the system console or running 'mattermost version'
  2. 2. Based on your current version, upgrade to the corresponding fixed release: 9.5.7, 9.7.6, 9.8.2, or a later version in your release line
  3. 3. If you are on version 9.9.0, upgrade to version 9.9.1 or later
  4. 4. After upgrade, verify that shared channels functionality continues to work correctly
  5. 5. Review audit logs to check for any unauthorized team or channel additions that may have occurred during the vulnerable period
Caveat Standard Mattermost upgrade considerations apply - review release notes for your version path for any breaking changes

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

Fix this in Mattermost Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,570
Get the upgrade done

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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-2024-39274 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