CVE-2026-23961: Mastodon is a free, open-source social network server based on ActivityPub. Mastodon allows server administrators to suspend remote users to prevent…

PriorityP432medium5.3CVSS 3.1

AVNACLPRNUINSUCNILAN

EPSS

0.40%

32.0th percentile

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.

Affected

6 ranges

Vendor	Product	Version range	Fixed in
joinmastodon	mastodon	< 4.3.18	4.3.18
joinmastodon	mastodon	>= 4.4.0 < 4.4.12	4.4.12
joinmastodon	mastodon	>= 4.5.0 < 4.5.5	4.5.5
mastodon	mastodon	< 4.3.18	4.3.18
mastodon	mastodon	—	—
mastodon	mastodon	—	—

Stop checking back — get the weekly exploitation signal.

Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.