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MastodonApplication · Joinmastodon

CVE-2026-23962

HIGH · 7.5 CVSS v3.1 Published 2026-01-22
Fix available
A fix is available. Upgrade to 4.3.18 / 4.4.12 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
Mastodon is a free, open-source social network server based on ActivityPub. Mastodon versions before v4.3.18, v4.4.12, and v4.5.5 do not have a limit on the maximum number of poll options for remote posts, allowing attackers to create polls with a very large amount of options, greatly increasing resource consumption. Depending on the number of poll options, an attacker can cause disproportionate resource usage in both Mastodon servers and clients, potentially causing Denial of Service either server-side or client-side. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.

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 before v4.3.18, v4.4.12, and v4.5.5 lack validation on the number of poll options in incoming ActivityPub (remote) posts, allowing attackers to create polls with an arbitrarily large number of options. This causes disproportionate resource consumption on both Mastodon servers and client applications, potentially leading to Denial of Service.

MitigationUpgrade Mastodon to version v4.3.18, v4.4.12, or v4.5.5 (whichever aligns with the current branch) to implement poll option limits and prevent resource exhaustion attacks.

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
MastodonApplication
Affected:< 4.3.18>= 4.4.0, < 4.4.12>= 4.5.0, < 4.5.5

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 installed Mastodon version via API
    Make a GET request to https://your-mastodon-instance.com/api/v1/instance and look at the 'version' field in the response
    Affected if Version is less than 4.3.18, or between 4.4.0 and 4.4.12, or between 4.5.0 and 4.5.5
  2. Confirm ActivityPub receive is enabled
    Check the mastodon configuration file (config/environments/production.rb or config/defaults.yml) for the 'activitypub' setting, or verify the instance accepts remote inbox requests
    Affected if ActivityPub reception is enabled (this is the default and required for federated operation)

You are affected if your Mastodon version falls within the affected ranges AND ActivityPub is enabled, which allows receiving remote posts.

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 4.3.18 / 4.4.12 / 4.5.5 or later
Fixed in 4.3.184.4.124.5.5
Interim mitigation

Upgrade Mastodon to version v4.3.18, v4.4.12, or v4.5.5 (whichever aligns with the current branch) to implement poll option limits and prevent resource exhaustion attacks.

Recommended fix High confidence

Upgrade to Mastodon v4.3.18, v4.4.12, or v4.5.5 (whichever corresponds to your current major version)

  1. 1. Check your current Mastodon version in the admin interface (Administration > Server > Activity) or by running `git -C /opt/mastodon rev-parse --short HEAD`
  2. 2. Based on your current version, identify the appropriate upgrade target: for 4.3.x go to 4.3.18; for 4.4.x go to 4.4.12; for 4.5.x go to 4.5.5
  3. 3. Back up your Mastodon database and configuration files before upgrading
  4. 4. For source installations: run `git fetch --tags` and `git checkout v<target-version>` followed by `bundle install` and `RAILS_ENV=production bundle exec rake db:migrate`
  5. 5. For Docker installations: update the image tag to the target version and recreate containers
  6. 6. Restart all Mastodon services (web, sidekiq, streaming)
  7. 7. Verify the upgrade was successful and poll functionality works correctly
Caveat Minor version upgrades typically have no 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.

Fix this in Mastodon Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

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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-2026-23962 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