# CVE-2026-28431: Misskey lacks proper authorization checks and input validation

> Attackers can access unauthorized data due to insufficient permission checks and input validation in Misskey servers.

- **Severity:** Critical 9.2 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Mar 2026
- **Updated:** 10 Mar 2026
- **Also known as:** GHSA-r33c-qg3g-v9cr

## What is CVE-2026-28431?

CVE-2026-28431 is a critical missing authorization vulnerability in misskey-dev misskey, published on 9 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Misskey is an open source, federated social media platform. All Misskey servers running versions 8.45.0 and later, but prior to 2026.3.1, contain a vulnerability that allows bad actors access to data that they ordinarily wouldn't be able to access due to insufficient permission checks and proper input validation. This vulnerability occurs regardless of whether federation is enabled or not. This vulnerability could lead to a significant data breach. This vulnerability is fixed in 2026.3.1.

Weakness: CWE-285 (Improper Authorization)

## Which versions are affected by CVE-2026-28431?

It affects 1 product.


Products: Misskey Misskey.

## How do I fix CVE-2026-28431?

No fix has been published for CVE-2026-28431 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-28431 being exploited?

There is no known exploitation of CVE-2026-28431 in the wild and no public exploit code.

## Other vulnerabilities in misskey-dev misskey

- [CVE-2025-25306](https://insights.sbomify.com/CVE-2025-25306/): Misskey's Incomplete Patch of CVE-2024-52591 Leads to Forgery of Federated Notes (critical 9.3)
- [CVE-2023-49079](https://insights.sbomify.com/CVE-2023-49079/): Misskey's missing signature validation allows arbitrary users to impersonate any remote user. (critical 9.3)
- [CVE-2023-52139](https://insights.sbomify.com/CVE-2023-52139/): Misskey vulnerable to improper authorization when accessing with third-party application (critical 9.1)
- [CVE-2024-52590](https://insights.sbomify.com/CVE-2024-52590/): Missing validation allows spoofed profiles in Misskey (high 8.8)
- [CVE-2024-52591](https://insights.sbomify.com/CVE-2024-52591/): Missing validation allows spoofed profiles and notes in Misskey (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-28431 and fix it if it is affected.

What it is: CVE-2026-28431 is a critical missing authorization vulnerability in misskey-dev misskey, published on 9 Mar 2026. 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-2026-28431 in the wild and no public exploit code.

Affected product: misskey-dev misskey. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-28431/ (Markdown: https://insights.sbomify.com/CVE-2026-28431/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-28431
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-28431
- OSV: https://osv.dev/vulnerability/CVE-2026-28431

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-28431/
Summaries are generated and may contain mistakes; the official description above is the record.