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Mattermost ServerApplication · Mattermost

CVE-2026-20719

HIGH · 7.5 CVSS v3.1 Published 2026-03-25
Fix available
A fix is available. Upgrade to 10.11.12 / 11.2.4 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 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to prevent rendering of external SVGs on link embeds which allows unauthenticated users to crash the Mattermost webapp and desktop app via creating an issue or PR on GitHub.. Mattermost Advisory ID: MMSA-2026-00595

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 prevent rendering of external SVG files in link embeds. An unauthenticated attacker can crash the Mattermost webapp or desktop app by creating a malicious GitHub issue or PR containing a crafted SVG URL that, when rendered as a link preview, triggers a crash.

MitigationBlock external SVG content from rendering in link previews by configuring content-type restrictions in the link preview processing logic, or apply vendor-supplied patch when available.

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, < 11.4.1

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. Check Mattermost Server version
    Run 'mattermost version' or check the System Console > About page for the server version number
    Affected if The installed version falls within >= 10.11.0 and < 10.11.12, OR >= 11.2.0 and < 11.2.4, OR >= 11.3.0 and < 11.3.2, OR >= 11.4.0 and < 11.4.1
  2. Verify link previews are enabled
    Navigate to System Console > Posts > Link Previews, or check the 'Enable Link Previews' setting in site configuration
    Affected if Link previews are turned ON in the server settings
  3. Confirm external URL previews are allowed
    Check if 'Enable server-side image linking' or similar external content settings are enabled in System Console > Posts > Link Previews, allowing preview generation for external URLs
    Affected if External URL link previews are permitted in the configuration

You are affected if your Mattermost Server version is in the affected ranges AND link previews for external URLs are enabled, as this allows malicious SVG content to be fetched and rendered, causing a crash.

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

Block external SVG content from rendering in link previews by configuring content-type restrictions in the link preview processing logic, or apply vendor-supplied patch when available.

Recommended fix High confidence

Upgrade to 10.11.12 (for 10.11.x), 11.2.4 (for 11.2.x), 11.3.2 (for 11.3.x), or 11.4.1 (for 11.4.x) - preferably upgrade to the latest stable branch (e.g., 11.x series)

  1. 1. Identify the currently running Mattermost Server version using the system console or mmctl CLI tool
  2. 2. Based on the current version, determine the appropriate upgrade path to the fixed release
  3. 3. Back up the Mattermost database and configuration files before upgrading
  4. 4. For installations using the mattermost-operator (Kubernetes), update the CustomResource to use the fixed version image
  5. 5. For installations using the tar.gz method, download the appropriate fixed release from mattermost.com and follow the upgrade instructions
  6. 6. For installations using the Mattermost Omnibus or Linux packages, update via the package manager (e.g., apt-get update && apt-get upgrade mattermost-server)
  7. 7. Verify the upgrade completed successfully by checking the server version in the system console
  8. 8. Test that link embeds no longer render external SVGs by sharing a link to an external SVG file
Caveat Review Mattermost release notes for your target version to check for any breaking changes or required migration steps before upgrading

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

Fix this in Mattermost Server Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,560.

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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-2026-20719 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