Vulnerability Description
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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Joinmastodon | Mastodon | < 4.3.18 |
Related Weaknesses (CWE)
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-6x3w-9g92-gvf3Vendor Advisory
FAQ
What is CVE-2026-23963?
CVE-2026-23963 is a vulnerability with a CVSS score of 4.3 (MEDIUM). 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,...
How severe is CVE-2026-23963?
CVE-2026-23963 has been rated MEDIUM with a CVSS base score of 4.3/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-23963?
Check the references section above for vendor advisories and patch information. Affected products include: Joinmastodon Mastodon.