Medium 5.3Published Jan 22, 2026

CVE-2026-23961Mastodon is a free, open-source social network server based on ActivityPub.

Updated under an hour ago (2026-10-19 06:30 UTC)

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It affects joinmastodon mastodon. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for joinmastodon mastodon

Exploited in the last 30 days

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.

CVSS: 5.3 MEDIUM (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness (CWE): CWE-863
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Not given
NVD analysis: Analyzed
Record last updated: Jun 17, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

joinmastodon mastodon joinmastodon:mastodon	before 4.3.18; from 4.4.0 before 4.4.12; from 4.5.0 before 4.5.5	NVD

References

https://github.com/mastodon/mastodon/releases/tag/v4.3.18release-notes
https://github.com/mastodon/mastodon/releases/tag/v4.4.12release-notes
https://github.com/mastodon/mastodon/releases/tag/v4.5.5release-notes
https://github.com/mastodon/mastodon/security/advisories/GHSA-5h2f-wg8j-xqwpvendor-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.