CVE-2018-21018: Joinmastodon Mastodon

Critical severity, CVSS 9.8. EPSS: 2.6% chance of exploitation in the next 30 days.

Mastodon before 2.6.3 mishandles timeouts of incompletely established sessions.

Affected products

• Joinmastodon Mastodon: before 2.6.3 (fixed in 2.6.3)

Published 2019-09-22. Last modified 2026-06-17.