Chassis Daemon UAF DoS in Junos OS before 22.4R3-S8
CVE-2026-21921 Published on January 15, 2026
Junos OS and Junos OS Evolved: When telemetry collectors are frequently subscribing and unsubscribing to sensors chassisd or rpd will crash
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.
Vulnerability Analysis
CVE-2026-21921 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
What is a Dangling pointer Vulnerability?
Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.
CVE-2026-21921 has been classified to as a Dangling pointer vulnerability or weakness.
Products Associated with CVE-2026-21921
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Affected Versions
Juniper Networks Junos OS:- Before 22.4R3-S8 is affected.
- Version 23.2 and below 23.2R2-S5 is affected.
- Version 23.4 and below 23.4R2 is affected.
- Before 22.4R3-S8-EVO is affected.
- Version 23.2 and below 23.2R2-S5-EVO is affected.
- Version 23.4 and below 23.4R2-EVO is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.