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.

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was seen during production usage.

This issue has been assigned CVE-2021-31376 .

The following software releases have been updated to resolve this specific issue: Junos OS 18.4R3-S8.

This issue is being tracked as 1565716 .

Software releases or updates are available for download at https://support.juniper.net/support/downloads/

There are no viable workarounds for this issue.

2021-10-13: Initial Publication.

• KB16613: Overview of the Juniper Networks SIRT Quarterly Security Bulletin Publication Process [juniper.net]
• KB16765: In which releases are vulnerabilities fixed? [juniper.net]
• KB16446: Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories [juniper.net]
• Report a Vulnerability - How to Contact the Juniper Networks Security Incident Response Team
• CVE-2021-31376: Packet Forwarding Engine manager (FXPC) process crashes when processing DHCPv6 packets