A Protection Mechanism Failure vulnerability in RPD (routing protocol daemon) of Juniper Networks Junos OS and Junos OS Evolved allows an adjacent unauthenticated attacker to cause established IS-IS adjacencies to go down by sending a spoofed hello PDU leading to a Denial of Service (DoS) condition.

Continued receipted of these spoofed PDUs will create a sustained Denial of Service (DoS) condition.

This issue affects:

Juniper Networks Junos OS

• All versions prior to 18.2R3-S8;
• 18.3 versions prior to 18.3R3-S5;
• 18.4 versions prior to 18.4R3-S9;
• 19.1 versions prior to 19.1R3-S7;
• 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 19.4R3-S3;
• 20.1 versions prior to 20.1R3;
• 20.2 versions prior to 20.2R3;
• 20.3 versions prior to 20.3R3;
• 20.4 versions prior to 20.4R2.

Juniper Networks Junos OS Evolved

• All versions prior to 20.4R2-EVO;
• 21.1 versions prior to 21.1R2-EVO.

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-2021-31362 .

The following software releases have been updated to resolve this specific issue in JUNOS OS: 18.2R3-S8, 18.3R3-S5, 18.4R3-S9, 19.1R3-S7, 19.2R1-S7, 19.2R3-S3, 19.3R2-S6, 19.3R3-S2, 19.4R3-S3, 20.1R3, 20.2R3, 20.3R3, 20.4R2, 21.1R1, and all subsequent releases.

The following software releases have been updated to resolve this specific issue in JUNOS OS Evolved: 20.4R2-EVO, 21.1R2-EVO, 21.2R1-EVO, and all subsequent releases.

This issue is being tracked as  1556575 .

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

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-2021-31362: Junos OS and Junos OS Evolved: An IS-IS adjacency might be taken down if a bad hello PDU is received for an existing adjacency causing a DoS