CVE-2026-22246

Description

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.

How to fix CVE-2026-22246

To remediate CVE-2026-22246, upgrade the affected package to a fixed version below.

—upgrade to 4.3.17 or later

Is CVE-2026-22246 being exploited?

Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.

Affected packages (1)

from 0, < 4.3.17, >= 4.4.0, < 4.4.11, >= 4.5.0, < 4.5.4

CVSS scores

Source	Version	Severity	Vector
osv	CVSS 3.1	MEDIUM4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N