CVE-2026-23961
MEDIUMCVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Lifecycle Timeline
2Description
Mastodon is a free, open-source social network server based on ActivityPub. Mastodon allows server administrators to suspend remote users to prevent interactions. However, some logic errors allow already-known posts from such suspended users to appear in timelines if boosted. Furthermore, under certain circumstances, previously-unknown posts from suspended users can be processed. This issue allows old posts from suspended users to occasionally end up on timelines on all Mastodon versions. Additionally, on Mastodon versions from v4.5.0 to v4.5.4, v4.4.5 to v4.4.11, v4.3.13 to v4.3.17, and v4.2.26 to v4.2.29, remote suspended users can partially bypass the suspension to get new posts in. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.
Analysis
Suspended remote users in Mastodon can bypass suspension restrictions and have their posts appear in timelines through boosting and post processing logic errors. This affects all Mastodon versions for older posts, with additional bypass capabilities in versions 4.5.0-4.5.4, 4.4.5-4.4.11, 4.3.13-4.3.17, and 4.2.26-4.2.29, allowing suspended users to inject new content into the system. …
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Remediation
Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.
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External POC / Exploit Code
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