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MattermostApplication

CVE-2024-39836

MEDIUM · 6.5 CVSS v3.1 Published 2024-08-22
Fix available
A fix is available. Upgrade to 9.5.8 / 9.8.3 or later.
See remediation →
74/100
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
Mattermost versions 9.9.x <= 9.9.1, 9.5.x <= 9.5.7, 9.10.x <= 9.10.0 and 9.8.x <= 9.8.2 fail to ensure that remote/synthetic users cannot create sessions or reset passwords, which allows the munged email addresses, created by shared channels, to be used to receive email notifications and to reset passwords, when they are valid, functional emails.

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 fails to properly restrict remote/synthetic users created through the shared channels feature from authenticating and resetting passwords. The 'munged' email addresses assigned to these synthetic users can function as valid email addresses, allowing them to receive notifications and complete password reset flows, leading to unauthorized account access.

MitigationUpgrade to Mattermost versions 9.9.2, 9.5.8, 9.10.1, 9.8.3 or later. These versions contain fixes to prevent remote/synthetic users from creating sessions or resetting passwords using their munged email addresses.

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, < 9.5.8>= 9.8.0, < 9.8.3>= 9.9.0, < 9.9.2>= 9.10.0, < 9.10.1

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
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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
    Run 'mmctl version' or look at the Mattermost System Console under About > Mattermost, or inspect the /opt/mattermost/version file
    Affected if The installed version falls within the affected ranges: 9.5.0-9.5.7, 9.8.0-9.8.2, 9.9.0-9.9.1, or 9.10.0
  2. Verify if Shared Channels feature is enabled
    Check Mattermost config.json for 'EnableSharedChannels' setting under 'ServiceSettings', or navigate to System Console > Channels > Enable Shared Channels
    Affected if Shared Channels is enabled and connected to at least one remote instance
  3. Identify remote users from shared channels
    Query the database: SELECT Username, Email, RemoteId FROM Users WHERE RemoteId IS NOT NULL; or use mmctl: 'mmctl user list --json' and filter for users with email addresses containing patterns like @remote.xxx
    Affected if There exist users with remote IDs or email addresses in the format used for shared channel participants (typically containing @proxy. or similar munged patterns)
  4. Check for password reset activity by remote users
    Review Mattermost logs for password reset events: grep -i 'password reset' /var/log/mattermost/*.log and correlate with remote user accounts
    Affected if Password reset tokens have been issued to or used by remote/synthetic user accounts

A user is affected if they run a vulnerable Mattermost version with Shared Channels enabled and have remote/synthetic users in their system who were able to receive password reset tokens or establish sessions.

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 9.5.8 / 9.8.3 / 9.9.2 or later
Fixed in 9.5.89.8.39.9.2
Interim mitigation

Upgrade to Mattermost versions 9.9.2, 9.5.8, 9.10.1, 9.8.3 or later. These versions contain fixes to prevent remote/synthetic users from creating sessions or resetting passwords using their munged email addresses.

Recommended fix High confidence

9.5.8, 9.8.3, 9.9.2, or 9.10.1 (depending on current version branch)

  1. Identify the currently installed Mattermost version from the affected list (9.5.0-9.5.7, 9.8.0-9.8.2, 9.9.0-9.9.1, or 9.10.0-9.10.0)
  2. Upgrade to the corresponding fixed version: 9.5.8 if on 9.5.x, 9.8.3 if on 9.8.x, 9.9.2 if on 9.9.x, or 9.10.1 if on 9.10.x
  3. Follow standard Mattermost upgrade procedures (backup database, test in staging environment before production)
  4. After upgrade, verify that remote/synthetic users (from shared channels) can no longer reset passwords or create sessions
Caveat Review Mattermost release notes for any breaking changes between your current version and the target fixed version

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
  • Testing4.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,720
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,752.

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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-2024-39836 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