Resource exhaustion in Joinmastodon Mastodon
CVE-2025-54879
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.
EPSS: 0.005 (42.0th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
Affected products
- Joinmastodon Mastodon
- Mastodon — versions >= 3.1.5, < 4.2.24, >= 4.3.0, < 4.3.11, >= 4.4.0, < 4.4.3
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Third Party Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC, Release Notes)
Frequently asked questions
- What is CVE-2025-54879?
- CVE-2025-54879 is a medium-severity vulnerability in Joinmastodon Mastodon, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 5.3/10. Published 2025-08-06.
- How severe is CVE-2025-54879?
- Medium severity. CVSS v3 base score is 5.3 out of 10.