CVE-2026-21921
- CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- Published: 2026-01-15T21:16:08.400
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.
Related CVE by CWE
No related CWE found.
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How to fix CVE-2026-21921
Description: 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 […]
Exploit Difficulty: EASY
⏱️ Time to exploit: < 1 hour
🛠️ Required skills: Basic web security knowledge
💰 Public exploits: Likely available
How to Fix:
- Check if you're running the affected product
- Update to the latest patched version
- If patching is not immediately possible: restrict network exposure, apply least-privilege access
- Test the fix in a staging environment first
- Review logs for signs of exploitation
- Monitor for IOCs (Indicators of Compromise)
- Enable automatic security updates
- Set up vulnerability monitoring
- Review and harden security configurations
Exploit Difficulty Assessment
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Detection Rules & IOCs
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No vendor/product data available.