Use After Free in Juniper Junos
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.
Vulnerability class: Use-After-Free
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.004 (29.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 30th percentile — 29.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000
Affected products
- Juniper Junos — versions 22.4, 23.2, 23.4
- Juniper Junos OS Evolved — versions 22.4, 23.2, 23.4
- Juniper Networks Junos OS — versions 0, 23.2, 23.4
- Juniper Networks Junos OS Evolved — versions 0, 23.2, 23.4
Weakness classification (CWE)
References
- supportportal.juniper.net/JSA106021 (vendor-advisory, Vendor Advisory)
- kb.juniper.net/JSA106021 (vendor-advisory, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-21921?
- CVE-2026-21921 is a medium-severity vulnerability in Juniper Junos, classified under Use After Free. CVSS score: 6.5/10. Published 2026-01-15.
- How severe is CVE-2026-21921?
- Medium severity. CVSS v3 base score is 6.5 out of 10.