CVE-2021-31353: Juniper Junos

High severity, CVSS 7.5. EPSS: 1.2% chance of exploitation in the next 30 days.

An Improper Handling of Exceptional Conditions vulnerability in Juniper Networks Junos OS and Junos OS Evolved allows an attacker to inject a specific BGP update, causing the routing protocol daemon (RPD) to crash and restart, leading to a Denial of Service (DoS). Continued receipt and processing of the BGP update will create a sustained Denial of Service (DoS) condition. This issue affects very specific versions of Juniper Networks Junos OS: 19.3R3-S2; 19.4R3-S3; 20.2 versions 20.2R2-S3 and later, prior to 20.2R3-S2; 20.3 versions 20.3R2 and later, prior to 20.3R3; 20.4 versions 20.4R2 and later, prior to 20.4R3; 21.1 versions prior to 21.1R2. Juniper Networks Junos OS 20.1 is not affected by this issue. This issue also affects Juniper Networks Junos OS Evolved: All versions prior to 20.4R2-S3-EVO, 20.4R3-EVO; 21.1-EVO versions prior to 21.1R2-EVO; 21.2-EVO versions prior to 21.2R2-EVO.

Affected products

• Juniper Junos: version 19.3 only; version 19.4 only; version 20.2 only; version 20.3 only; version 20.4 only; version 21.1 only
• Juniper Junos OS Evolved: up to and including 20.3; version 20.4 only; version 21.1 only; version 21.2 only

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