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.

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.

Published 2025-08-06 · last modified 2026-06-17.

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.

EPSS exploit prediction

EPSS: 0.005 (42.9th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 43rd percentile — 42.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000

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)

CWE-770 — Allocation of Resources Without Limits or Throttling

References

github.com/mastodon/mastodon/security/advisories/GHSA-84ch-6436-c7mg (Third Party Advisory)
github.com/mastodon/mastodon/commit/e2592419d93fb41be03c2f3ff6a122fecb0e0952 (Patch)
github.com/mastodon/mastodon/releases/tag/v4.4.3 (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.