CVE-2023-36461: Joinmastodon Mastodon

High severity, CVSS 7.5. EPSS: 1.3% chance of exploitation in the next 30 days.

Mastodon is a free, open-source social network server based on ActivityPub. When performing outgoing HTTP queries, Mastodon sets a timeout on individual read operations. Prior to versions 3.5.9, 4.0.5, and 4.1.3, a malicious server can indefinitely extend the duration of the response through slowloris-type attacks. This vulnerability can be used to keep all Mastodon workers busy for an extended duration of time, leading to the server becoming unresponsive. Versions 3.5.9, 4.0.5, and 4.1.3 contain a patch for this issue.

Affected products

• Joinmastodon Mastodon: before 3.5.9 (fixed in 3.5.9); from 4.0.0, before 4.0.5 (fixed in 4.0.5); from 4.1.0, before 4.1.3 (fixed in 4.1.3)

Published 2023-07-06. Last modified 2026-06-17.