# CVE-2021-33959: Denial of service in n/a

> Attackers can launch DDoS reflection attacks against Plex media servers, causing service disruption for users.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 Jan 2023
- **Updated:** 4 Apr 2025
- **Also known as:** GHSA-8788-3qj3-84j7

## What is CVE-2021-33959?

CVE-2021-33959 is a high-severity denial of service vulnerability in n/a, published on 18 Jan 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Plex media server 1.21 and before is vulnerable to ddos reflection attack via plex service.

Weakness: CWE-346 (Origin Validation Error)

## Which versions are affected by CVE-2021-33959?

It affects 1 product.


Products: Plex Media Server.

## How do I fix CVE-2021-33959?

No fix has been published for CVE-2021-33959 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-33959 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-33959 exists.

Public exploit code:

- CVE-2021-33959 (github_poc): https://github.com/lixiang957/CVE-2021-33959

## Other vulnerabilities in n/a

- [CVE-2026-96656](https://insights.sbomify.com/CVE-2026-96656/): Plex Media Server External Control of File Name or Path (high 8.6, exploited in the wild)
- [CVE-2020-5741](https://insights.sbomify.com/CVE-2020-5741/): Plex Media Server Remote Code Execution (high 7.2, exploited in the wild)
- [CVE-2026-96654](https://insights.sbomify.com/CVE-2026-96654/): Plex Media Server Improper Neutralization of Encoded URI Schemes in a Web Page (medium 6.9, exploited in the wild)
- [CVE-2026-96652](https://insights.sbomify.com/CVE-2026-96652/): Plex Media Server Server-Side Request Forgery (SSRF) (medium 5.3, exploited in the wild)
- [CVE-2026-96655](https://insights.sbomify.com/CVE-2026-96655/): Plex Media Server Server-Side Request Forgery (SSRF) (medium 5.3, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-33959 and fix it if it is affected.

What it is: CVE-2021-33959 is a high-severity denial of service vulnerability in n/a, published on 18 Jan 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-33959 exists.

Affected product: n/a. 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-2021-33959/ (Markdown: https://insights.sbomify.com/CVE-2021-33959/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-33959
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-33959
- OSV: https://osv.dev/vulnerability/CVE-2021-33959

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-33959/
Summaries are generated and may contain mistakes; the official description above is the record.