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CWE-248Weakness · CWE-248

CVE-2026-50129

HIGH · 7.5 CVSS v3.1 Published 2026-06-24
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
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
Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.5.11, 4.4.18, and 4.3.24, a DoS can be triggered by (Uncaught Exception vulerability), due to missing exception handling in the math sanitizer. Malformed <math> nodes can result in a DoS of a whole server or targeted users services, depending on the type of action that includes the malformed nodes and the services interacting with it. This vulnerability is fixed in 4.5.11, 4.4.18, and 4.3.24.

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

Mastodon versions prior to 4.5.11, 4.4.18, and 4.3.24 contain a missing exception handler in the math sanitizer. When malformed <math> nodes are processed, an uncaught exception is thrown, causing a denial of service that can affect the entire server or specific user services.

MitigationUpgrade Mastodon to version 4.5.11, 4.4.18, or 4.3.24 (or later) which contain the fix for proper exception handling in the math sanitizer.

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

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 Mastodon version
    Check the version displayed on your Mastodon instance about page (usually at /about) or query the instance API at /api/v1/instance. The version is also visible in the footer of the web interface.
    Affected if The version shown is lower than 4.3.24, 4.4.18, or 4.5.11 depending on your release branch (any version prior to these respective cutoffs).
  2. Confirm math content processing is active
    Mastodon processes <math> tags through its HTML sanitizer when rendering user-posted content (statuses, profiles, etc). This feature is enabled by default for all instances that accept HTML content in posts. No special configuration toggle is needed.
    Affected if Your instance accepts and renders user-posted content containing HTML, which includes math tags. The vulnerability triggers during sanitization of such content.
  3. Verify vulnerable code path exists
    If you have shell access, navigate to the Mastodon source directory and locate the math sanitizer file (typically in lib/mastodon/sanitize_css_math.rb or similar math-related sanitizer modules). Check if exception handling for malformed math nodes is present - the fixed version includes begin/rescue blocks around math node parsing.
    Affected if The math sanitizer code lacks exception handling around math node processing, allowing uncaught exceptions to crash the server.

You are affected if your Mastodon version is prior to 4.3.24, 4.4.18, or 4.5.11 and your instance processes user-submitted HTML content containing <math> tags.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Mastodon to version 4.5.11, 4.4.18, or 4.3.24 (or later) which contain the fix for proper exception handling in the math sanitizer.

Recommended fix High confidence

Mastodon 4.5.11 (or 4.4.18 / 4.3.24 depending on your current release branch)

  1. 1. Determine your current Mastodon version by checking the version file or admin interface
  2. 2. Create a full backup of your Mastodon database and file storage before upgrading
  3. 3. Stop the Mastodon services (web, sidekiq, streaming)
  4. 4. Update Mastodon to version 4.5.11 (or 4.4.18 / 4.3.24 depending on your release line) using your deployment method
  5. 5. Run database migrations with `RAILS_ENV=production bundle exec rails db:migrate`
  6. 6. Precompile assets with `RAILS_ENV=production bundle exec rails assets:precompile`
  7. 7. Restart all Mastodon services
  8. 8. Verify the upgrade was successful and the application is functioning normally
Caveat Patch releases typically have no breaking changes, but review the release notes for any deprecation notices

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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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-2026-50129 in production — separate from our analysis above.

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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