Legal HoldApplication · Mattermost

CVE-2026-3524

HIGH · 8.8 CVSS v3.1 Published 2026-04-06

Fix available

A fix is available. Upgrade to 1.1.5 or later.

See remediation →

94/100

Remediation priority · Urgent

Remotely reachable Zero-click

Official description

NVD · unedited

Mattermost Plugin Legal Hold versions <=1.1.4 fail to halt request processing after a failed authorization check in ServeHTTP which allows an authenticated attacker to access, create, download, and delete legal hold data via crafted API requests to the plugin's endpoints. Mattermost Advisory ID: MMSA-2026-00621

Technical summary

dbcve analysis · high confidence

The Mattermost Legal Hold plugin versions <=1.1.4 contain an authorization bypass vulnerability where the ServeHTTP function fails to halt request processing after a failed authorization check. This allows any authenticated user to access, create, download, and delete sensitive legal hold data through crafted API requests to the plugin's endpoints.

MitigationUpgrade the Mattermost Legal Hold plugin to version 1.1.5 or later to remediate the authorization bypass. Organizations should also review access logs for suspicious legal hold API activity.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions

NVD · CPE data

Legal HoldApplication

Affected:< 1.1.5

CVSS breakdown

From the vector

Attack vector: Network
Complexity: Low
Privileges: Low
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Am I affected?

dbcve checks

Work through these to decide whether this CVE applies to you.

Verify if Legal Hold plugin is installed

Use Mattermost CLI (mmctl plugin list) or navigate to System Console > Plugins > Plugin Management to list installed plugins. Look for 'Legal Hold' or 'com.mattermost.legal-hold' in the list.

Affected if The Legal Hold plugin appears in the installed plugins list.
Determine the installed Legal Hold plugin version

In System Console > Plugins > Plugin Management, click on the Legal Hold plugin to view its version details. Alternatively, inspect the plugin manifest or use mmctl plugin get <plugin-id>.

Affected if The installed version is 1.1.4 or earlier.
Confirm the plugin is enabled

In System Console > Plugins > Plugin Management, verify that the Legal Hold plugin shows as 'Enabled' rather than 'Disabled' or not configured.

Affected if The plugin status shows as Enabled.
Review API access logs for legal hold endpoints

Search Mattermost audit logs or server logs for requests to /plugins/com.mattermost.legal-hold/* endpoints. Look for API calls from users who should not have legal hold permissions (non-admin, non-legal team accounts).

Affected if There are API requests to legal hold plugin endpoints from users lacking explicit legal hold permissions.

A user is affected if the Legal Hold plugin is installed, enabled, and running at version 1.1.4 or earlier.

Generated from the published advisory. Verify against your own configuration.

Remediation

dbcve · scoped

Upgrade available Upgrade to 1.1.5 or later

Fixed in 1.1.5

Interim mitigation

Upgrade the Mattermost Legal Hold plugin to version 1.1.5 or later to remediate the authorization bypass. Organizations should also review access logs for suspicious legal hold API activity.

Recommended fix Moderate confidence

Legal Hold plugin version >1.1.4 (latest available version from Mattermost Marketplace)

Navigate to Mattermost System Console
Go to Plugin Management or Marketplace
Find the 'Legal Hold' plugin in the installed plugins list
Check if an update is available for the Legal Hold plugin
Click to update/upgrade the Legal Hold plugin to the latest available version
Verify the plugin was updated successfully
Test that the authorization checks are now properly enforced

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

Fix this in Legal Hold Scoped from the published advisory

Consultation1.0 h
Implementation1.0 h
Testing3.0 h
Review / QA1.0 h

6.0 hours of engineering $1,010

Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,616.

Scan for this in your stack

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References

Primary sources

mattermost.comVendor Advisory
nvd.nist.govNVD record

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-3524 in production — separate from our analysis above.

Notes0 Guidelines

Know something about CVE-2026-3524?

The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.

The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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

At a glance

A fix existsUpgrade to 1.1.5 or later

Severity 8.8 High

Exploit likelihood EPSS, next 30 days 0.4%

Affects: Legal Hold

Remediation

A high-priority fix

Fix this in Legal Hold 6 hrs · Moderate

Typical engagement from $1,010

Get a fix See the full breakdown ↓

A high-priority vulnerability. Send your environment and a specialist will scope CVE-2026-3524 and return a fixed quote and timeline.

You’ll deal with our team directly and deploy the reviewed fix to staging first — never straight to production.

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.

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.

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.

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.

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.

Check your environment

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.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

No notes yet

Official description

Technical summary

Affected products & versions

CVSS breakdown

Am I affected?

Remediation

References