CVE-2026-27468 Mastodon may allow unconfirmed FASP to make subscriptions
Unapproved FASP clients can subscribe to events and request backfill, causing information leaks and denial of service on Mastodon servers with experimental features enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-27468?
CVE-2026-27468 is a medium-severity missing authorization vulnerability in mastodon, published on 24 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-862
Which versions are affected by CVE-2026-27468?
1 open source package ship an affected version, including mastodon. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
mastodon Bitnami | From 4.4.0 | 4.4.14, 4.5.7 |
Products include Joinmastodon Mastodon.
How do I fix CVE-2026-27468?
Upgrade mastodon to a fixed version for your release line: 4.4.14 or 4.5.7.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-27468 being exploited?
There is no known exploitation of CVE-2026-27468 in the wild and no public exploit code.
Other vulnerabilities in mastodon
- CVE-2023-36460 Mastodon vulnerable to arbitrary file creation through media attachments
- CVE-2022-2166 Improper Restriction of Excessive Authentication Attempts in mastodon/mastodon
- CVE-2022-24307 Missing authorization in n/a
- CVE-2018-21018 Auth bypass in n/a
- CVE-2024-23832 Mastodon Remote user impersonation and takeover
Sources
Also known as BIT-mastodon-2026-27468, GHSA-qgmm-vr4c-ggjg.