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

> Attackers can bypass rate limits on the setup endpoint to spam arbitrary email addresses, causing resource exhaustion and service disruption.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Feb 2025
- **Updated:** 27 Feb 2025
- **Also known as:** BIT-mastodon-2025-27157, GHSA-v39f-c9jj-8w7h

## What is CVE-2025-27157?

CVE-2025-27157 is a medium-severity denial of service vulnerability in mastodon, published on 27 Feb 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2025-27157?

1 open source package ship an affected version, including mastodon. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mastodon` | Bitnami | From 4.2.0 | 4.3.4 |

Products: Joinmastodon Mastodon.

## How do I fix CVE-2025-27157?

Upgrade mastodon to 4.3.4 or later.

## Is CVE-2025-27157 being exploited?

There is no known exploitation of CVE-2025-27157 in the wild and no public exploit code.

## Other vulnerabilities in mastodon

- [CVE-2023-36460](https://insights.sbomify.com/CVE-2023-36460/): Mastodon vulnerable to arbitrary file creation through media attachments (critical 10.0)
- [CVE-2022-2166](https://insights.sbomify.com/CVE-2022-2166/): Improper Restriction of Excessive Authentication Attempts in mastodon/mastodon (critical 9.8)
- [CVE-2022-24307](https://insights.sbomify.com/CVE-2022-24307/): Missing authorization in n/a (critical 9.8)
- [CVE-2018-21018](https://insights.sbomify.com/CVE-2018-21018/): Auth bypass in n/a (critical 9.8)
- [CVE-2024-23832](https://insights.sbomify.com/CVE-2024-23832/): Mastodon Remote user impersonation and takeover (critical 9.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-27157 and fix it if it is affected.

What it is: CVE-2025-27157 is a medium-severity denial of service vulnerability in mastodon, published on 27 Feb 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-27157 in the wild and no public exploit code.

Affected packages and fixed versions:
- mastodon (Bitnami): affected from 4.2.0; fixed in 4.3.4

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-27157/ (Markdown: https://insights.sbomify.com/CVE-2025-27157/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-27157
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-27157
- OSV: https://osv.dev/vulnerability/CVE-2025-27157

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-27157/
Summaries are generated and may contain mistakes; the official description above is the record.