Cyber Resilience

CVE-2021-33959

HighPublic PoC

Published: 18 January 2023

Published
18 January 2023
Modified
04 April 2025
KEV Added
Patch
CVSS Score v3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS Score 0.0559 90.5th percentile
Risk Priority 18 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2021-33959 is a high-severity Origin Validation Error (CWE-346) vulnerability in Plex Media Server. Its CVSS base score is 7.5 (High).

Operationally, ranked in the top 9.5% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

EU & UK References

Vulnerability details

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

CWE(s)

Related Threats

No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.

Affected Assets

plex
media server
≤ 1.21

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

addresses: CWE-346

Requires unique identification of the service before communications, addressing failures to validate the origin of the interaction.

addresses: CWE-346

Trusted path establishment enforces validation that the communication originates from and reaches only the intended trusted system components.

addresses: CWE-346

Enforces validation of the true origin of DNS responses via signatures and chain-of-trust mechanisms.

addresses: CWE-346

Enforces origin validation of name/address data, eliminating reliance on unverified or impersonated DNS sources.

addresses: CWE-346

Mandates origin validation so that only legitimate endpoints can continue the authenticated session.

References