CVE-2026-23963
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.
Does this matter?
Lower severity and a low EPSS score (0.32%). Track it; it rarely justifies an emergency change on its own.
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 3.1
- 6.5 MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 0.32% probability · 24th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-770
- Affected
- joinmastodon/mastodon
- Source
- security-advisories@github.com
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
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.