CVE-2026-21921: Juniper Junos

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

A Use After Free vulnerability in the chassis daemon (chassisd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker authenticated with low privileges to cause a Denial-of-Service (DoS). When telemetry collectors are frequently subscribing and unsubscribing to sensors continuously over a long period of time, telemetry-capable processes like chassisd, rpd or mib2d will crash and restart, which - depending on the process - can cause a complete outage until the system has recovered. This issue affects:  Junos OS:  * all versions before 22.4R3-S8, * 23.2 versions before 23.2R2-S5, * 23.4 versions before 23.4R2; Junos OS Evolved: * all versions before 22.4R3-S8-EVO, * 23.2 versions before 23.2R2-S5-EVO, * 23.4 versions before 23.4R2-EVO.

Affected products

• Juniper Junos: before 22.4 (fixed in 22.4); version 22.4 only; version 23.2 only; version 23.4 only
• Juniper Junos OS Evolved: before 22.4 (fixed in 22.4); version 22.4 only; version 23.2 only; version 23.4 only

Published 2026-01-15. Last modified 2026-06-17.