CVE-2026-41259: Mastodon is a free, open-source social network server based on ActivityPub. Prior to v4.5.9, v4.4.16, and v4.3.22…
CVE-2026-41259 · Severity: high · CVSS 7.5 · Published 2026-04-23
Mastodon is a free, open-source social network server based on ActivityPub. Prior to v4.5.9, v4.4.16, and v4.3.22, Mastodon allows restricting new user sign-up based on e-mail domain names, and performs basic validation on e-mail addresses, but fails to restrict characters that are interpreted differently by some mailing servers. This vulnerability is fixed in v4.5.9, v4.4.16, and v4.3.22.
No. Junglewise Threat Intelligence has no report of CVE-2026-41259 being exploited in the wild.
How severe is CVE-2026-41259?
High severity, with a CVSS score of 7.5, published 23 April 2026.
Which products and versions are affected?
Joinmastodon Mastodon. The advisory does not name versions.
Is there a fix for CVE-2026-41259?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
Am I affected by CVE-2026-41259?
Check whether you run Joinmastodon Mastodon. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.