CVE-2021-31362: Juniper Junos

Medium severity, CVSS 6.5. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Juniper Junos: up to and including 18.1; version 18.2 only; version 18.3 only; version 18.4 only; version 19.1 only; version 19.2 only; …
• Juniper Junos OS Evolved: up to and including 20.3; version 20.4 only; version 21.1 only

Published 2021-10-19. Last modified 2026-06-17.