CVE-2026-27468
highpriority · track · 33OT risk · elevatedEPSS 0.003 · 20 %ileEUUSEPSS · scored 2026-10-27
Mastodon is a free, open-source social network server based on ActivityPub. FASP registration requires manual approval by an administrator. In versions 4.4.0 through 4.4.13 and 4.5.0 through 4.5.6, actions performed by a FASP to subscribe to account/content lifecycle events or to backfill content did not check properly whether the FASP was actually approved. This only affects Mastodon servers that have opted in to testing the experimental FASP feature by setting the environment variable `EXPERIMENTAL_FEATURES` to a value including `fasp`. An attacker can make subscriptions and request content backfill without approval by an administrator. Done once, this leads to minor information leak of URIs that are publicly available anyway. But done several times this is a serious vector for DOS, putting pressure on the sidekiq worker responsible for the `fasp` queue. The fix is included in the 4.4.14 and 4.5.7 releases. Admins that are actively testing the experimental "fasp" feature should update their systems. Servers not using the experimental feature flag `fasp` are not affected.
cvss
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 4.8–8.2
ssvc
A stakeholder decision — act, attend, or track — from exploitation and impact.
weaknesses
The CWE weakness classes this flaw belongs to.
affected products (6)
Products and version ranges known to be affected.
advisories (1)
Vendor and ecosystem advisories describing this.
- BIT-mastodon-2026-27468Mastodon may allow unconfirmed FASP to make subscriptions2026-03-02vendor · osvUS
Mastodon is a free, open-source social network server based on ActivityPub. FASP registration requires manual approval by an administrator. In versions 4.4.0 through 4.4.13 and 4.5.0 through 4.5.6, actions performed by a FASP to subscribe to account/content lifecycle events or to backfill content did not check properly whether the FASP was actually approved. This only affects Mastodon servers that have opted in to testing the experimental FASP feature by setting the environment variable `EXPERIMENTAL_FEATURES` to a value including `fasp`. An attacker can make subscriptions and request content backfill without approval by an administrator. Done once, this leads to minor information leak of URIs that are publicly available anyway. But done several times this is a serious vector for DOS, putting pressure on the sidekiq worker responsible for the `fasp` queue. The fix is included in the 4.4.14 and 4.5.7 releases. Admins that are actively testing the experimental "fasp" feature should update their systems. Servers not using the experimental feature flag `fasp` are not affected.
also known as (3)
Other names and identifiers for this entity.
sources
Which sources assert this record, and when.
references (7)
External citations — patches, advisories, analysis.
- https://github.com/mastodon/mastodon/commit/6ba6285a73c3a8b281123814d45f534e3bcebb96cnnvd
- https://github.com/mastodon/mastodon/releasesPatchcnnvd
- https://github.com/mastodon/mastodon/security/advisories/GHSA-qgmm-vr4c-ggjgcnnvd
- https://github.com/mastodon/mastodon/commit/6ba6285a73c3a8b281123814d45f534e3bcebb96enisa_euvd
- https://github.com/mastodon/mastodon/security/advisories/GHSA-qgmm-vr4c-ggjgenisa_euvd
- https://github.com/mastodon/mastodon/commit/6ba6285a73c3a8b281123814d45f534e3bcebb96Patchnvd
- https://github.com/mastodon/mastodon/security/advisories/GHSA-qgmm-vr4c-ggjgPatchVendor Advisorynvd
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