Vulnerability · Published Apr 23, 2026 · Assigned by GitHub_M

CVE-2026-41259Mastodon: Insufficient verification of email addresses

High 8.2

In plain English

A high-severity security flaw in mastodon from mastodon. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 12% of all known vulnerabilities).

Severity (CVSS 4.0)8.2High

Exploit odds (30 days)0.2%top 88.3% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

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.

Affected products (as reported)

Vendor	Product	Versions
mastodon	mastodon	< 4.3.22>= 4.4.0-beta.1, < 4.4.16>= 4.5.0-beta.1, < 4.5.9

Weakness: CWE-841 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

References

https://github.com/mastodon/mastodon/security/advisories/GHSA-5r37-qpwq-2jhh x_refsource_CONFIRM