CVE-2025-54879: Joinmastodon Mastodon

High severity, CVSS 7.5. EPSS: 0.6% chance of exploitation in the next 30 days.

Mastodon is a free, open-source social network server based on ActivityPub Mastodon which facilitates LDAP configuration for authentication. In versions 3.1.5 through 4.2.24, 4.3.0 through 4.3.11 and 4.4.0 through 4.4.3, Mastodon's rate-limiting system has a critical configuration error where the email-based throttle for confirmation emails incorrectly checks the password reset path instead of the confirmation path, effectively disabling per-email limits for confirmation requests. This allows attackers to bypass rate limits by rotating IP addresses and send unlimited confirmation emails to any email address, as only a weak IP-based throttle (25 requests per 5 minutes) remains active. The vulnerability enables denial-of-service attacks that can overwhelm mail queues and facilitate user harassment through confirmation email spam. This is fixed in versions 4.2.24, 4.3.11 and 4.4.3.

Affected products

• Joinmastodon Mastodon: from 3.1.5, before 4.2.24 (fixed in 4.2.24); from 4.3.0, before 4.3.11 (fixed in 4.3.11); from 4.4.0, before 4.4.3 (fixed in 4.4.3)

Published 2025-08-06. Last modified 2026-06-17.