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Mattermost ServerApplication · Mattermost

CVE-2026-3114

MEDIUM · 6.5 CVSS v3.1 Published 2026-03-26
Fix available
A fix is available. Upgrade to 10.11.12 / 11.2.4 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 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to validate decompressed archive entry sizes during file extraction which allows authenticated users with file upload permissions to cause a denial of service via crafted zip archives containing highly compressed entries (zip bombs) that exhaust server memory.. Mattermost Advisory ID: MMSA-2026-00598

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 validate decompressed archive entry sizes during file extraction, allowing authenticated users with file upload permissions to upload crafted zip archives (zip bombs) containing highly compressed entries that expand to massive sizes when decompressed, exhausting server memory and causing denial of service.

MitigationUpgrade Mattermost to version 11.4.1, 11.3.2, 11.2.4, 10.11.12 or later. Consider restricting file upload permissions or implementing file size limits as a compensating control until patching is complete.

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:>= 10.11.0, < 10.11.12>= 11.2.0, < 11.2.4>= 11.3.0, < 11.3.2= 11.4.0

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
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/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 Mattermost Server version
    Run 'mattermost version' or check the system diagnostic page in the Mattermost UI under Product menu > Mattermost > About. On Linux, also check /opt/mattermost/version.py or the package metadata.
    Affected if Installed version falls within ranges: 10.11.0 through 10.11.11, 11.2.0 through 11.2.3, 11.3.0 through 11.3.1, or exactly 11.4.0
  2. Verify file upload is enabled
    In Mattermost UI, navigate to System Console > Environment > File Storage, or check the 'FileSettings.EnableFileAttachments' setting in config.json. Also verify user roles include upload permissions.
    Affected if File attachments are enabled and the user has upload permissions (default for authenticated users with access to channels)
  3. Check current server memory usage and upload logs
    Review Mattermost server logs for signs of memory pressure or failed upload requests. Run 'top' or 'free -m' on the server host. Check for large zip file upload attempts in /var/log/mattermost/ or the configured log path.
    Affected if Server shows high memory usage coinciding with zip file uploads, or logs contain entries for large uncompressed sizes relative to compressed upload sizes

You are affected if your Mattermost Server version is 10.11.0-10.11.11, 11.2.0-11.2.3, 11.3.0-11.3.1, or exactly 11.4.0 AND file uploads are enabled for authenticated users.

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 10.11.12 / 11.2.4 / 11.3.2 or later
Fixed in 10.11.1211.2.411.3.2
Interim mitigation

Upgrade Mattermost to version 11.4.1, 11.3.2, 11.2.4, 10.11.12 or later. Consider restricting file upload permissions or implementing file size limits as a compensating control until patching is complete.

Recommended fix High confidence

10.11.12 for 10.11.x line; 11.2.4 for 11.2.x line; 11.3.2 for 11.3.x line; 11.4.1 or later for 11.4.x line

  1. 1. Identify the currently running Mattermost Server version using the system console or mmctl command: mmctl version
  2. 2. Based on your current version, plan the upgrade to the fixed release: For 10.11.x: upgrade to 10.11.12; For 11.2.x: upgrade to 11.2.4; For 11.3.x: upgrade to 11.3.2; For 11.4.0: upgrade to 11.4.1 or later
  3. 3. Back up the Mattermost database and file storage before upgrading
  4. 4. Download the appropriate Mattermost Server release from the official Mattermost downloads page
  5. 5. Follow the standard Mattermost upgrade procedure for your deployment type (e.g., for Docker: stop container, pull new image, restart; for Ansible/helm: run upgrade playbook or helm upgrade)
  6. 6. Verify the upgrade was successful by checking the server version in the system console under About > Mattermost
  7. 7. Test file upload functionality to ensure the server is operational
Caveat Standard Mattermost minor version upgrades typically maintain backward compatibility, but always review the changelog for any breaking changes before upgrading

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

Fix this in Mattermost Server Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing5.0 h
  • Review / QA3.0 h
17.0 hours of engineering $2,970
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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-2026-3114 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