CVE-2026-22246
MEDIUMCVSS Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Lifecycle Timeline
3Description
Mastodon is a free, open-source social network server based on ActivityPub. Mastodon 4.3 added notifications of severed relationships, allowing end-users to inspect the relationships they lost as the result of a moderation action. The code allowing users to download lists of severed relationships for a particular event fails to check the owner of the list before returning the lost relationships. Any registered local user can access the list of lost followers and followed users caused by any severance event, and go through all severance events this way. The leaked information does not include the name of the account which has lost follows and followers. This has been fixed in Mastodon v4.3.17, v4.4.11 and v4.5.4.
Analysis
Mastodon versions prior to 4.3.17, 4.4.11, and 4.5.4 fail to validate ownership when retrieving severed relationship lists, allowing any authenticated user to enumerate all lost followers and followed accounts across all severance events. This information disclosure vulnerability affects multi-user Mastodon instances where relationship changes due to moderation actions are visible to unauthorized users. …
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Remediation
Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Vendor patch is available.
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