CVE-2021-33959Known exploitationPublic exploitNetwork attack vector

DDoS amplification via spoofed SSDP discovery requests

Published Jan 18, 2023 · Updated Apr 4, 2025

SSDP reflection in Plex Media Server 1.21 and earlier allows remote attackers to amplify DDoS traffic via crafted UDP requests. The UPnP-enabled service-registration responder on UDP ports 32410 and 32414 answers spoofed M-SEARCH requests, sending larger responses to the forged source address. Exposure requires a public-facing host or explicit forwarding of the discovery ports; the attack disrupts third-party networks without reading private data or changing Plex accounts.

CVSS severity7.5
High
EPSS probability15.04%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSDP reflection in Plex Media Server 1.21 and earlier allows remote attackers to amplify DDoS traffic via crafted UDP requests. The UPnP-enabled service-registration responder on UDP ports 32410 and 32414 answers spoofed M-SEARCH requests, sending larger responses to the forged source address. Exposure requires a public-facing host or explicit forwarding of the discovery ports; the attack disrupts third-party networks without reading private data or changing Plex accounts.

The record

CVE
CVE-2021-33959
Published
Jan 18, 2023
Updated
Apr 4, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-400, CWE-346, T1498.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 18, 2023CVE publishedPublication date reported by the CVE source.
  2. Apr 4, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
CWE-346Origin Validation Error
T1498.002Reflection Amplification

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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