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CWE-354Weakness · CWE-354

CVE-2026-50128

MEDIUM · 5.3 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 →
62/100
Remediation priority · Elevated
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. From 4.3.0 until 4.5.11 and 4.4.18, Mastodon has a feature to let websites credit authors of their articles. To prevent false attribution claims, Mastodon uses the attributionDomains JSON-LD term, however, an error in how it is defined makes Linked Data Signatures on the toot:attributionDomains property ineffective. An attacker can arbitrarily modify the attributionDomains value of a legitimately signed Update activity and bypass Mastodon’s signature verification. This vulnerability is fixed in 4.5.11 and 4.4.18.

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's attributionDomains JSON-LD term, used to prevent false attribution claims in its author credit feature, is incorrectly defined. This error renders Linked Data Signatures on the toot:attributionDomains property ineffective, allowing attackers to arbitrarily modify the attributionDomains value of a legitimately signed Update activity and bypass Mastodon's signature verification.

MitigationUpgrade Mastodon to version 4.5.11, 4.4.18, or later to apply the security fix.

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
Low
Availability
None

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

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 Mastodon installation
    Locate Mastodon instance by checking for known files such as config/environment.rb, or identify via package manager (dpkg -l mastodon, rpm -qa mastodon), gem list mastodon, or checking running processes for mastodon references
    Affected if Mastodon software is not found on the system
  2. Determine installed Mastodon version
    Run mastodon --version, check gem list mastodon, examine package manager output, or inspect version file in the Mastodon directory if present
    Affected if Unable to retrieve version information from the Mastodon installation
  3. Compare version against fixed releases
    Compare the installed version string to the known fixed versions 4.5.11 and 4.4.18. Versions below 4.5.11 (in the 4.5.x line) or below 4.4.18 (in the 4.4.x line) are affected
    Affected if Installed version is earlier than 4.5.11 or earlier than 4.4.18
  4. Verify ActivityPub federation is enabled
    Confirm the instance has federation enabled by checking admin settings or testing federation with a known remote account (the vulnerability affects signed activities which are a core ActivityPub feature)
    Affected if ActivityPub federation is active (most Mastodon instances have this enabled by default)

The instance is affected if it runs a Mastodon version earlier than 4.5.11 or earlier than 4.4.18 and has ActivityPub federation enabled, as the flawed JSON-LD term allows signature bypass on attributionDomains values.

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 later to apply the security fix.

Recommended fix High confidence

Mastodon 4.5.11 (latest stable) or 4.4.18 (LTS)

  1. Backup your Mastodon database and any custom configurations before starting the upgrade
  2. Review the release notes for versions 4.5.11 and 4.4.18 to understand any required configuration changes
  3. If running Mastodon 4.3.0 through 4.5.10, upgrade to version 4.5.11 (or later if available)
  4. If running an LTS version from 4.3.0 through 4.4.17, upgrade to version 4.4.18 (or later if available)
  5. Run database migrations with `RAILS_ENV=production bundle exec rails db:migrate`
  6. Precompile assets with `RAILS_ENV=production bundle exec rails assets:precompile`
  7. Restart all Mastodon services (Puma, Sidekiq, streaming) to apply changes
  8. Verify the upgrade by checking the Mastodon admin panel or running `bin/mastodon --version`
Caveat Review release notes; major version upgrades may include breaking changes to the API or configuration

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
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2026-50128 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