CVE-2026-23963 MEDIUM

CVE-2026-23963: Mastodon missing length limits on list names, filter names, and filter keywords

Vendor Mastodon
Product mastodon
Weakness CWE-770 · Uncontrolled resource consumption
Published January 22, 2026
Last update January 22, 2026

CVSS base score

4.3/10
Attack vector Network
Attack complexity Low
Privileges required Low
User interaction None
Confidentiality None
Integrity None

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

What the vulnerability does

01Description

Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.5.5, 4.4.12, and 4.3.18, the server does not enforce a maximum length for the names of lists or filters, or for filter keywords, allowing any user to set an arbitrarily long string as the name or keyword. Any local user can abuse the list or filter fields to cause disproportionate storage and computing resource usage. They can additionally cause their own web interface to be unusable, although they must intentionally do this to themselves or unknowingly approve a malicious API client. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.

Key dates

02Disclosure timeline

January 22, 2026 CVE published
January 22, 2026 Record updated