CVE-2021-0233Network attack vector

Sustained service interruption via high-rate packet processing

Published Apr 22, 2021 · Updated Sep 16, 2024

Denial of service in Juniper Networks Junos OS 17.4 before 17.4R3-S2 allows remote attackers to crash ACX500 and ACX4000 FFEBs. The packet-processing path incompletely filters repeated special packet elements and consumes resources until the Forwarding Engine Board crashes. Unauthenticated network reachability is sufficient, and continued packet receipt sustains the outage without reported confidentiality or integrity impact.

CVSS severity7.5
High
EPSS probability0.96%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Juniper Networks Junos OS 17.4 before 17.4R3-S2 allows remote attackers to crash ACX500 and ACX4000 FFEBs. The packet-processing path incompletely filters repeated special packet elements and consumes resources until the Forwarding Engine Board crashes. Unauthenticated network reachability is sufficient, and continued packet receipt sustains the outage without reported confidentiality or integrity impact.

The record

CVE
CVE-2021-0233
Published
Apr 22, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-400, CWE-794, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=17.4 <17.4R3-S2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=17.4 <17.4R3-S2

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5Juniper NetworksCVSS: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 exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
CWE-794Incomplete Filtering of Multiple Instances of Special Elements
T1499Endpoint 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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