Medium severity · published Jan 22, 2026
CVE-2026-23961
Mastodon may allow a remote suspension bypass
5.3
CVSS
0.4%
EPSS
No
On KEV
Description
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 38% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
mastodon · mastodon
< 4.3.18; >= 4.4.0, < 4.4.12; >= 4.5.0, < 4.5.5 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-23961
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-23961
Release Notes
https://github.com/mastodon/mastodon/releases/tag/v4.3.18
Release Notes
https://github.com/mastodon/mastodon/releases/tag/v4.4.12
Release Notes
https://github.com/mastodon/mastodon/releases/tag/v4.5.5
Vendor Advisory
https://github.com/mastodon/mastodon/security/advisories/GHSA-5h2f-wg8j-xqwp
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