Auth bypass in Joinmastodon Mastodon
CVE-2026-33869
Mastodon is a free, open-source social network server based on ActivityPub. In versions on the 4.5.x branch prior to 4.5.8 and on the 4.4.x branch prior to 4.4.15, an attacker that knows of a quote before it has reached a server can prevent it from being correctly processed on that server. The vulnerability has been patched in Mastodon 4.5.8 and 4.4.15. Mastodon 4.3 and earlier are not affected because they do not support quotes.
Vulnerability class: Broken Access Control
Published · last modified .
CVSS v3 metric
CVSS v3 base score 4.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L.
EPSS exploit prediction
EPSS: 0.003 (16.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 17th percentile — 16.5% 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: 0.003 · change: +0.001
Affected products
- Joinmastodon Mastodon
- Mastodon — versions >= 4.5.0, < 4.5.8, >= 4.4.0, < 4.4.15
Weakness classification (CWE)
References
- github.com/mastodon/mastodon/security/advisories/GHSA-q4g8-82c5-9h33 (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-33869?
- CVE-2026-33869 is a medium-severity vulnerability in Joinmastodon Mastodon, classified under Incorrect Authorization. CVSS score: 4.8/10. Published 2026-03-27.
- How severe is CVE-2026-33869?
- Medium severity. CVSS v3 base score is 4.8 out of 10.