What is CVE-2025-27157?

CVE-2025-27157 is a medium-severity vulnerability in Joinmastodon Mastodon, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 5.3/10. Published 2025-02-27.

How severe is CVE-2025-27157?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Resource exhaustion in Joinmastodon Mastodon

CVE-2025-27157

Mastodon is a self-hosted, federated microblogging platform. Starting in version 4.2.0 and prior to versions 4.2.16 and 4.3.4, the rate limits are missing on `/auth/setup`. Without those rate limits, an attacker can craft requests that will send an email to an arbitrary addresses. Versions 4.2.16 and 4.3.4 fix the issue.

Published 2025-02-27 · 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: 0.004 (27.9th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 28th percentile — 27.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000

Affected products

Joinmastodon Mastodon
Mastodon — versions >= 4.2.0, < 4.2.16, >= 4.3.0, < 4.3.4

Weakness classification (CWE)

CWE-770 — Allocation of Resources Without Limits or Throttling

References

github.com/mastodon/mastodon/security/advisories/GHSA-v39f-c9jj-8w7h (Vendor Advisory)
github.com/mastodon/mastodon/commit/06f879ce9bea195344ac9f71e6799eea500628ec (Patch)

Frequently asked questions

What is CVE-2025-27157?: CVE-2025-27157 is a medium-severity vulnerability in Joinmastodon Mastodon, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 5.3/10. Published 2025-02-27.
How severe is CVE-2025-27157?: Medium severity. CVSS v3 base score is 5.3 out of 10.