CVE-2026-41259 Mastodon: Insufficient verification of email addresses
Attackers can bypass email domain restrictions during sign-up by using characters interpreted differently by mail servers, allowing unauthorized account creation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-41259?
CVE-2026-41259 is a high-severity vulnerability in mastodon, published on 23 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-841
Which versions are affected by CVE-2026-41259?
1 open source package ship an affected version, including mastodon. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
mastodon Bitnami | All versions | 4.3.22, 4.4.16, 4.5.9 |
Products include Joinmastodon Mastodon.
How do I fix CVE-2026-41259?
Upgrade mastodon to a fixed version for your release line: 4.3.22, 4.4.16 or 4.5.9.
Is CVE-2026-41259 being exploited?
There is no known exploitation of CVE-2026-41259 in the wild and no public exploit code.
Other vulnerabilities in mastodon
- CVE-2023-36460 Mastodon vulnerable to arbitrary file creation through media attachments
- CVE-2022-2166 Improper Restriction of Excessive Authentication Attempts in mastodon/mastodon
- CVE-2022-24307 Missing authorization in n/a
- CVE-2018-21018 Auth bypass in n/a
- CVE-2024-23832 Mastodon Remote user impersonation and takeover
Sources
Also known as BIT-mastodon-2026-41259, GHSA-5r37-qpwq-2jhh.