# CVE-2025-27399: Mastodon's domain blocks & rationales ignore user approval when visibility set as "users"

> Unapproved users can view private domain block rationales when visibility is restricted to logged-in users, exposing sensitive moderation data.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **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-2025-27399, GHSA-94h4-fj37-c825

## What is CVE-2025-27399?

CVE-2025-27399 is a medium-severity missing authorization 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. In versions prior to 4.1.23, 4.2.16, and 4.3.4, when the visibility for domain blocks/reasons is set to "users" (localized English string: "To logged-in users"), users that are not yet approved can view the block reasons. Instance admins that do not want their domain blocks to be public are impacted. Versions 4.1.23, 4.2.16, and 4.3.4 fix the issue.

Weakness: CWE-285 (Improper Authorization), CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2025-27399?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mastodon` | Bitnami | All versions | 4.3.4 |

Products: Joinmastodon Mastodon.

## How do I fix CVE-2025-27399?

Upgrade mastodon to 4.3.4 or later.

## Is CVE-2025-27399 being exploited?

There is no known exploitation of CVE-2025-27399 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-2025-27399 and fix it if it is affected.

What it is: CVE-2025-27399 is a medium-severity missing authorization 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-2025-27399 in the wild and no public exploit code.

Affected packages and fixed versions:
- mastodon (Bitnami): affected all versions; 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-2025-27399/ (Markdown: https://insights.sbomify.com/CVE-2025-27399/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-27399
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-27399
- OSV: https://osv.dev/vulnerability/CVE-2025-27399

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-27399/
Summaries are generated and may contain mistakes; the official description above is the record.