Use-after-free in Junos OS and Junos OS Evolved - CVE-2026-21921
Published: January 20, 2026
Vulnerability identifier: #VU121680
CSH Severity: Medium
CVSS v4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-21921
CWE-ID: CWE-416
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote user to perform a denial of service (DoS) attack.
The vulnerability exists due to use after free error in the chassis daemon (chassisd). A remote user can 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.
Affected software
Junos OS
Junos OS Evolved
Junos OS Evolved
How to mitigate CVE-2026-21921
Install updates from vendor's website.
Junos OS - addressed in versions 22.4R3-S8, 23.2R2-S5, 23.4R2, 24.2R1
Junos OS Evolved - addressed in versions 22.4R3-S8-EVO, 23.2R2-S5-EVO, 23.4R2-EVO, 24.2R1-EVO
Junos OS Evolved - addressed in versions 22.4R3-S8-EVO, 23.2R2-S5-EVO, 23.4R2-EVO, 24.2R1-EVO