CVE-2026-21921

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.