CVE-2021-0234Network attack vector

Packet disruption via unstarted DDoS protection daemon

Published Apr 22, 2021 · Updated Sep 17, 2024

Improper initialization in Juniper Networks Junos OS on QFX5100-96S devices allows remote attackers to disrupt packet handling during DDoS attacks. On affected QFX 5e Series images, the jddosd daemon does not start, so CLI changes to DDoS-protection limits never reach the packet forwarding engine and only its default limits remain active. The condition is limited to QFX5100-96S devices; traffic exceeding the unchanged defaults causes CPU-bound packets to be throttled or dropped.

CVSS severity5.8
Medium
EPSS probability0.95%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper initialization in Juniper Networks Junos OS on QFX5100-96S devices allows remote attackers to disrupt packet handling during DDoS attacks. On affected QFX 5e Series images, the jddosd daemon does not start, so CLI changes to DDoS-protection limits never reach the packet forwarding engine and only its default limits remain active. The condition is limited to QFX5100-96S devices; traffic exceeding the unchanged defaults causes CPU-bound packets to be throttled or dropped.

The record

CVE
CVE-2021-0234
Published
Apr 22, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-665, T1498
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=17.3 <17.3R3-S10
  2. Affected versionversion=17.4 <17.4R3-S4
  3. Affected versionversion=18.1 <18.1R3-S10
  4. Affected versionversion=18.2 <18.2R3-S3
  5. Affected versionversion=18.3 <18.3R3-S2
  6. Affected versionversion=18.4 <18.4R2-S4, 18.4R3-S1
  7. Affected versionversion=19.1 <19.1R3, 19.1R3-S4
  8. Affected versionversion=19.2 <19.2R2
  9. Affected versionversion=19.3 <19.3R3
  10. Affected versionversion=19.4 <19.4R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=17.3 <17.3R3-S10; version=17.4 <17.4R3-S4; version=18.1 <18.1R3-S10; version=18.2 <18.2R3-S3; version=18.3 <18.3R3-S2; version=18.4 <18.4R2-S4, 18.4R3-S1; version=19.1 <19.1R3, 19.1R3-S4; version=19.2 <19.2R2; version=19.3 <19.3R3; version=19.4 <19.4R2

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
5.8Juniper NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L

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 exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-665Improper Initialization
T1498Network Denial of Service

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

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Your stack

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