# 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…

Source: https://junglewise.ai/threats/cve-2026-41259-mastodon-is-a-free-open-source-social-network-server-based-on  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-23  
License: CC BY 4.0 with a link back

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.

Technologies: [Joinmastodon Mastodon](https://junglewise.ai/threats/technologies/joinmastodon-mastodon). Vendors: [Joinmastodon](https://junglewise.ai/threats/vendors/joinmastodon).

## Quick answers

**Is CVE-2026-41259 exploited in the wild?** 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.

## Affected products

- Joinmastodon Mastodon

## Related threats

- [Mastodon is a free, open-source social network server based on ActivityPub. Versions 4.2.27 and prior, 4.3.0-beta.1…](https://junglewise.ai/threats/cve-2025-67500-mastodon-is-a-free-open-source-social-network-server-based-on)
- [Mastodon is a free, open-source social network server based on ActivityPub. In Mastodon version 4.4, support for…](https://junglewise.ai/threats/cve-2025-62605-mastodon-is-a-free-open-source-social-network-server-based-on)