Auth bypass in Joinmastodon Mastodon
CVE-2026-23964
Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.5.5, 4.4.12, and 4.3.18, an insecure direct object reference in the web push subscription update endpoint lets any authenticated user update an…
Vulnerability class: Broken Access Control
EPSS: 0.002 (9.5th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.
Affected products
- Joinmastodon Mastodon
- Mastodon — versions < 4.3.18, >= 4.4.0, < 4.4.12, >= 4.5.0, < 4.5.5
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
- security-advisories@github.com (x_refsource_MISC, Release Notes)
- security-advisories@github.com (x_refsource_MISC, Release Notes)
- security-advisories@github.com (x_refsource_MISC, Release Notes)
Frequently asked questions
- What is CVE-2026-23964?
- CVE-2026-23964 is a medium-severity vulnerability in Joinmastodon Mastodon, classified under Incorrect Authorization. CVSS score: 6.5/10. Published 2026-01-22.
- How severe is CVE-2026-23964?
- Medium severity. CVSS v3 base score is 6.5 out of 10.