No exploitation reported

CVE-2021-31376

No exploitation reported by the sources we read.

Published2021-10-19
WeaknessCWE-20

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

An Improper Input Validation vulnerability in Packet Forwarding Engine manager (FXPC) process of Juniper Networks Junos OS allows an attacker to cause a Denial of Service (DoS) by sending specific DHCPv6 packets to the device and crashing the FXPC service. Continued receipt and processing of this specific packet will create a sustained Denial of Service (DoS) condition. This issue affects only the following platforms in ACX Series: ACX500, ACX1000, ACX1100, ACX2100, ACX2200, ACX4000, ACX5048, ACX5096 devices. Other ACX platforms are not affected from this issue. This issue affects Juniper Networks Junos OS on ACX500, ACX1000, ACX1100, ACX2100, ACX2200, ACX4000, ACX5048, ACX5096: 18.4 version 18.4R3-S7 and later versions prior to 18.4R3-S8. This issue does not affect: Juniper Networks Junos OS 18.4 versions prior to 18.4R3-S7 on ACX500, ACX1000, ACX1100, ACX2100, ACX2200, ACX4000, ACX5048, ACX5096.

Timeline

dates in UTC

2021-10-1919:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-31376?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-31376?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Juniper junosversion to verify

Branch	Affected	Fixed in	Source
18.4	= 18.4	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

kb.juniper.netVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CNACVSS 3.17.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
CNAweakness (CWE)CWE-20read 2026-10-23
NVDweakness (CWE)CWE-20read 2026-10-23
FIRST EPSSEPSS score1.0 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2021-10-19
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-31376?

Is CVE-2021-31376 actively exploited?

Active exploitation of CVE-2021-31376 has not been confirmed. Its EPSS score was 1.0% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-31376?

CVE-2021-31376 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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