An Uncontrolled Resource Consumption vulnerability in the kernel of Juniper Networks JUNOS OS allows an unauthenticated network based attacker to cause 100% CPU load and the device to become unresponsive by sending a flood of traffic to the out-of-band management ethernet port.

Continued receipted of a flood will create a sustained Denial of Service (DoS) condition. Once the flood subsides the system will recover by itself.

An indication that the system is affected by this issue would be that kernel and netisr process are shown to be using a lot of CPU cycles like in the following example output:

This issue affects Juniper Networks JUNOS OS on EX2300 Series, EX3400 Series, and ACX710:

• All versions prior to 18.1R3-S13;
• 18.2 versions prior to 18.2R3-S8;
• 18.3 versions prior to 18.3R3-S5;
• 18.4 versions prior to 18.4R2-S8, 18.4R3-S9;
• 19.1 versions prior to 19.1R3-S5;
• 19.2 versions prior to 19.2R1-S7, 19.2R3-S3;
• 19.3 versions prior to 19.3R2-S6, 19.3R3-S2;
• 19.4 versions prior to 19.4R1-S4, 19.4R3-S3;
• 20.1 versions prior to 20.1R2-S2, 20.1R3;
• 20.2 versions prior to 20.2R3;
• 20.3 versions prior to 20.3R2-S1, 20.3R3;
• 20.4 versions prior to 20.4R2.

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-2021-31368 .

The following software releases have been updated to resolve this specific issue: 18.1R3-S13, 18.3R3-S5, 18.4R2-S8, 18.4R3-S9, 19.1R3-S5, 19.2R1-S7, 19.2R3-S3, 19.3R2-S6, 19.3R3-S2, 19.4R1-S4, 19.4R3-S3, 20.1R2-S2, 20.1R3, 20.2R3, 20.3R2-S1, 20.3R3, 20.4R2, 21.1R1, and all subsequent releases.

This issue is being tracked as  1536800 .

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-2021-31368: Junos OS: EX2300 Series, EX3400 Series, and ACX710 might become unresponsive if the out-of-band management port receives a flood of traffic