# CVE-2021-39195: Server-Side Request Forgery vulnerability in misskey

> Attackers can exploit Server-Side Request Forgery in Misskey to disclose non-public information from the internal network.

- **Severity:** High 7.7 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 7 Sep 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-mqv7-gxh4-r5vf

## What is CVE-2021-39195?

CVE-2021-39195 is a high-severity server-side request forgery vulnerability in misskey-dev misskey, published on 7 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Misskey is an open source, decentralized microblogging platform. In affected versions a Server-Side Request Forgery vulnerability exists in "Upload from URL" and remote attachment handling. This could result in the disclosure of non-public information within the internal network. This has been fixed in 12.90.0. However, if you are using a proxy, you will need to take additional measures. As a workaround this exploit may be avoided by appropriately restricting access to private networks from the host where the application is running.

Weakness: CWE-918 (Server-Side Request Forgery)

## Which versions are affected by CVE-2021-39195?

It affects 1 product.


Products: Misskey Misskey.

## How do I fix CVE-2021-39195?

No fix has been published for CVE-2021-39195 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-39195 being exploited?

There is no known exploitation of CVE-2021-39195 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-2026-28431](https://insights.sbomify.com/CVE-2026-28431/): Misskey lacks proper authorization checks and input validation (critical 9.2)
- [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)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-39195 and fix it if it is affected.

What it is: CVE-2021-39195 is a high-severity server-side request forgery vulnerability in misskey-dev misskey, published on 7 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-39195 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-2021-39195/ (Markdown: https://insights.sbomify.com/CVE-2021-39195/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-39195
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-39195
- OSV: https://osv.dev/vulnerability/CVE-2021-39195

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-39195/
Summaries are generated and may contain mistakes; the official description above is the record.