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Mattermost ServerApplication · Mattermost

CVE-2026-24458

HIGH · 7.5 CVSS v3.1 Published 2026-03-16
Fix available
A fix is available. Upgrade to 10.11.11 / 11.2.3 or later.
See remediation →
84/100
Remediation priority · High
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 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly handle very long passwords, which allows an attacker to overload the server CPU and memory via executing login attempts with multi-megabyte passwords. Mattermost Advisory ID: MMSA-2026-00587

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 enforce password length limits during authentication, allowing attackers to submit multi-megabyte passwords that cause excessive CPU and memory consumption on the server, resulting in denial of service.

MitigationUpgrade Mattermost to the latest patched version. As an interim measure, implement password length validation at a reverse proxy or WAF level to block abnormally large authentication requests.

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, < 10.11.11>= 11.2.0, < 11.2.3>= 11.3.0, < 11.3.1

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
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/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. Identify installed Mattermost Server version
    Run 'mattermost version' or check the admin console under System Console > About, or inspect the version file in the Mattermost installation directory
    Affected if Version is 10.11.0 through 10.11.10, 11.2.0 through 11.2.2, or 11.3.0 (all affected ranges)
  2. Confirm password length validation is not enforced in application
    Check Mattermost configuration file (config.json) for 'PasswordSettings.MinLength' or similar password policy settings; verify in System Console > Authentication > Password that no maximum length is set
    Affected if No password length maximum is configured or enforced at the Mattermost application level (this is the vulnerable state)
  3. Determine if external validation layer exists
    Inspect reverse proxy (nginx, apache, etc.) or WAF configuration for request body size limits or explicit password field length restrictions on the /login endpoint
    Affected if No reverse proxy or WAF is present, or no explicit password length limits are configured at the proxy level (leaving the server exposed to oversized password payloads)
  4. Verify authentication endpoint accepts oversized payloads
    If permitted in your environment, attempt a login with a password exceeding normal lengths (e.g., 10KB+) and monitor server CPU/memory response, or review access logs for unusually large POST request sizes to /api/v4/users/login
    Affected if The server accepts and processes authentication requests with multi-kilobyte or larger password values without rejecting them

A user is affected if their Mattermost Server version falls within the affected ranges (10.11.0-10.11.10, 11.2.0-11.2.2, or 11.3.0) AND no password length validation exists at either the application level or an upstream proxy/WAF layer.

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 10.11.11 / 11.2.3 / 11.3.1 or later
Fixed in 10.11.1111.2.311.3.1
Interim mitigation

Upgrade Mattermost to the latest patched version. As an interim measure, implement password length validation at a reverse proxy or WAF level to block abnormally large authentication requests.

Recommended fix High confidence

Upgrade to 10.11.11+ (if on 10.11.x), 11.2.3+ (if on 11.2.x), or 11.3.1+ (if on 11.3.x)

  1. 1. Identify the currently installed Mattermost Server version using the system console or CLI
  2. 2. Based on your current version, plan the upgrade: if running 10.11.x, upgrade to 10.11.11 or later; if running 11.2.x, upgrade to 11.2.3 or later; if running 11.3.x, upgrade to 11.3.1 or later
  3. 3. Back up your Mattermost database and configuration files before upgrading
  4. 4. Follow Mattermost's standard upgrade procedure for your deployment type (e.g., using mattermostctl or package manager)
  5. 5. After upgrade, verify the server is operational and test login functionality
Caveat Point releases typically have minimal breaking changes; review Mattermost release notes for any noted changes

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
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,130
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,408.

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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-2026-24458 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