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CWE-354Weakness · CWE-354

CVE-2026-48028

MEDIUM · 6.5 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 →
74/100
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. Prior to 4.5.10, 4.4.17, and 4.3.23, Mastodon's normalization of incoming activities signed with Linked-Data Signatures does not sufficiently protect the activities from a certain class of spoofing, allowing threat actors to remove JSON entries from valid signed activities from a third-party actor. This vulnerability is fixed in 4.5.10, 4.4.17, and 4.3.23.

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 ActivityPub signature verification for Linked-Data Signatures (LDS) has a flaw in its normalization process. The normalization does not sufficiently protect JSON entries from removal, allowing a threat actor to strip certain fields from a validly signed activity while preserving a seemingly valid signature. This enables spoofing of third-party activities through improper canonicalization during signature validation.

MitigationUpgrade Mastodon to version 4.5.10, 4.4.17, or 4.3.23 to receive the patch that fixes the Linked-Data Signature normalization logic.

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
Low

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

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 the installed Mastodon version
    Run `git describe --tags` in the Mastodon installation directory, or check the VERSION file at the root of the installation, or look at the admin dashboard under /about/more
    Affected if The version is below 4.3.23, 4.4.17, or 4.5.10 (for example 4.3.0 through 4.3.22, or 4.4.0 through 4.4.16, or 4.5.0 through 4.5.9)
  2. Confirm ActivityPub is enabled
    Check the Mastodon configuration file (config/environments/production.rb or config/settings.yml) for the ActivityPub enabled setting, or inspect the web server responses to verify the system is accepting ActivityPub deliveries
    Affected if ActivityPub is enabled and the server accepts federated content from other ActivityPub servers (this is the default configuration for most Mastodon instances)
  3. Verify signature verification is in use
    Review the Mastodon logs (log/production.log) for incoming activities with signature validation, or check if the instance communicates with other federated servers by examining the Sidekiq queue for incoming federation jobs
    Affected if The instance processes signed activities from other ActivityPub servers (which is standard behavior for any federated Mastodon instance)

The instance is affected if it runs any Mastodon version below 4.3.23, 4.4.17, or 4.5.10 AND has ActivityPub enabled to receive federated content from other servers.

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 4.5.10, 4.4.17, or 4.3.23 to receive the patch that fixes the Linked-Data Signature normalization logic.

Recommended fix High confidence

Mastodon 4.5.10, 4.4.17, or 4.3.23 (depending on your current version branch)

  1. Identify your current Mastodon version using the admin interface or the /api/v1/instance endpoint
  2. Determine which upgrade path applies: if currently on 4.5.x, upgrade to 4.5.10; if on 4.4.x, upgrade to 4.4.17; if on 4.3.x or earlier, upgrade to 4.3.23 or a later stable release
  3. Review the Mastodon upgrade guide at https://docs.joinmastodon.org/admin/upgrading/
  4. Back up your Mastodon database and uploaded files before proceeding
  5. Stop the Mastodon services (web, sidekiq, streaming)
  6. Update Mastodon using your package manager or by pulling the new release: `git fetch && git checkout v<new-version>`
  7. Run database migrations: `RAILS_ENV=production bundle exec rails db:migrate`
  8. Precompile assets: `RAILS_ENV=production bundle exec rails assets:precompile`
Caveat Minor version upgrades typically do not include breaking changes, but review the release notes for your target version before upgrading

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,100
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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-2026-48028 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