CVE-2021-31376Network attack vector

FXPC crash via specific DHCPv6 packets

Published Oct 19, 2021 · Updated Sep 16, 2024

Improper input validation in Juniper Networks Junos OS 18.4R3-S7 allows remote attackers to crash FXPC with specific DHCPv6 packets. The Packet Forwarding Engine manager processes the crafted DHCPv6 input without adequate validation, causing the FXPC service to terminate. The packet must reach an affected ACX Series device, and continued delivery sustains the service interruption.

CVSS severity7.5
High
EPSS probability1.02%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Juniper Networks Junos OS 18.4R3-S7 allows remote attackers to crash FXPC with specific DHCPv6 packets. The Packet Forwarding Engine manager processes the crafted DHCPv6 input without adequate validation, causing the FXPC service to terminate. The packet must reach an affected ACX Series device, and continued delivery sustains the service interruption.

The record

CVE
CVE-2021-31376
Published
Oct 19, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-20, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 19, 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=18.4 <18.4R3-S7 changes=[{"at":"18.4R3-S7","status":"affected"},{"at":"18.4R3-S8","status":"unaffected"}]

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=18.4 <18.4R3-S7 changes=[{"at":"18.4R3-S7","status":"affected"},{"at":"18.4R3-S8","status":"unaffected"}]

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.

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No observations available

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

Weakness, pattern, technique

CWE-20Improper Input Validation
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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