Vulnerability in Joinmastodon Mastodon
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, 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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
EPSS exploit prediction
EPSS: 0.004 (28.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 29th percentile — 28.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.002
Affected products
- Joinmastodon Mastodon
- Mastodon — versions < 4.3.22, >= 4.4.0-beta.1, < 4.4.16, >= 4.5.0-beta.1, < 4.5.9
Weakness classification (CWE)
References
- github.com/mastodon/mastodon/security/advisories/GHSA-5r37-qpwq-2jhh (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-41259?
- CVE-2026-41259 is a high-severity vulnerability in Joinmastodon Mastodon, classified under Improper Enforcement of Behavioral Workflow. CVSS score: 7.5/10. Published 2026-04-23.
- How severe is CVE-2026-41259?
- High severity. CVSS v3 base score is 7.5 out of 10.