CVE-2021-0237

Sustained service interruption via Layer 2 frames

Published Apr 22, 2021 · Updated Sep 17, 2024

Denial of service in Juniper Networks Junos OS allows attackers to restart FXPC by sending specific frames on an adjacent Layer 2 network. Juniper has not disclosed how the Packet Forwarding Engine manager processes those frames incorrectly before it crashes and automatically restarts. Exposure requires an affected EX4300-MP, EX4600, EX4650, or QFX5K Virtual Chassis with a specific Layer 2 circuit configuration; continued frames sustain the service interruption.

CVSS severity6.5
Medium
EPSS probability0.38%
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 allows attackers to restart FXPC by sending specific frames on an adjacent Layer 2 network. Juniper has not disclosed how the Packet Forwarding Engine manager processes those frames incorrectly before it crashes and automatically restarts. Exposure requires an affected EX4300-MP, EX4600, EX4650, or QFX5K Virtual Chassis with a specific Layer 2 circuit configuration; continued frames sustain the service interruption.

The record

CVE
CVE-2021-0237
Published
Apr 22, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
T1499.004
Attack vector
adjacent
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=15.1 <15.1R7-S9
  2. Affected versionversion=17.3 <17.3R3-S11
  3. Affected versionversion=17.4 <17.4R2-S13, 17.4R3-S4, 17.4R3-S5
  4. Affected versionversion=18.2 <18.2R3-S8
  5. Affected versionversion=18.3 <18.3R3-S4
  6. Affected versionversion=18.4 <18.4R2-S7, 18.4R3-S6
  7. Affected versionversion=19.1 <19.1R3-S4
  8. Affected versionversion=19.2 <19.2R1-S6, 19.2R3-S1
  9. Affected versionversion=19.3 <19.3R3-S1
  10. Affected versionversion=19.4 <19.4R2-S4, 19.4R3-S1
  11. Affected versionversion=20.1 <20.1R2
  12. Affected versionversion=20.2 <20.2R2, 20.2R3
  13. Affected versionversion=20.3 <20.3R1-S2, 20.3R2

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=15.1 <15.1R7-S9; version=17.3 <17.3R3-S11; version=17.4 <17.4R2-S13, 17.4R3-S4, 17.4R3-S5; version=18.2 <18.2R3-S8; version=18.3 <18.3R3-S4; version=18.4 <18.4R2-S7, 18.4R3-S6; version=19.1 <19.1R3-S4; version=19.2 <19.2R1-S6, 19.2R3-S1; version=19.3 <19.3R3-S1; version=19.4 <19.4R2-S4, 19.4R3-S1; version=20.1 <20.1R2; version=20.2 <20.2R2, 20.2R3; version=20.3 <20.3R1-S2, 20.3R2

Published CVSS scores

6.5Juniper Networks, Inc.CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.3NIST NVDAV:A/AC:L/Au:N/C:N/I:N/A:P

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

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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