What is CVE-2021-33959?

CVE-2021-33959 is a high-severity vulnerability in Plex Media Server, classified under Origin Validation Error. CVSS score: 7.5/10. Published 2023-01-18.

How severe is CVE-2021-33959?

High severity. CVSS v3 base score is 7.5 out of 10.

Is CVE-2021-33959 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Plex Media Server

CVE-2021-33959

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

Published 2023-01-18 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.150 (96.6th percentile), scored 2026-09-24.

Moderate probability of exploitation in the next 30 days — watch for active exploitation reports. 97th percentile — 96.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.150 · newest: 0.150 · change: 0.000

Affected products

Plex Media Server

Weakness classification (CWE)

CWE-346 — Origin Validation Error

Public proof-of-concept exploits

References

www.freebuf.com/articles/web/260338.html (Technical Description, Exploit, Third Party Advisory)
github.com/lixiang957/CVE-2021-33959 (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2021-33959?: CVE-2021-33959 is a high-severity vulnerability in Plex Media Server, classified under Origin Validation Error. CVSS score: 7.5/10. Published 2023-01-18.
How severe is CVE-2021-33959?: High severity. CVSS v3 base score is 7.5 out of 10.
Is CVE-2021-33959 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.