CVE-2026-23963: Mastodon missing length limits on list names, filter names, and filter keywords
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.
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-23963?
CVE-2026-23963 has a moderate severity due to missing length limits allowing potential denial of service attacks.
How do I fix CVE-2026-23963?
To resolve CVE-2026-23963, upgrade your Mastodon server to versions 4.5.5, 4.4.12, or 4.3.18 or later.
What versions of Mastodon are affected by CVE-2026-23963?
CVE-2026-23963 affects Mastodon versions prior to 4.5.5, 4.4.12, and 4.3.18.
What components of Mastodon are impacted by CVE-2026-23963?
CVE-2026-23963 impacts the length limits on list names, filter names, and filter keywords.
Is there a security advisory for CVE-2026-23963?
Yes, CVE-2026-23963 is documented in security advisories on the official Mastodon GitHub repository.