🛡️ CVE-2026-27468 — mastodon

🟡 CVSS 5.0 — Medium ✅ No Known Exploit CWE-862 OSV
5.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Mastodon may allow unconfirmed FASP to make subscriptions

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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality low, integrity none, availability high.

Weakness class

CVE-2026-27468 is classified as CWE-862: Missing Authorization. No authorisation check is performed before carrying out a restricted action.

Affected software

CVE-2026-27468 is recorded against 1 package.

  • mastodon

Timeline and source

Published on 2 March 2026 and last revised on 17 June 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from OSV.

References

github.com (Web)
github.com (Web)
nvd.nist.gov (Web)

Details

Severity MEDIUM
CVSS Score 5.0
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
CWE CWE-862
Public Exploit ✅ No
Source OSV
Published 2026-03-02
Updated 2026-08-12
Modified 2026-06-17

Affected Packages

Software From version Fixed in
mastodon — —

Similar Threats

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