CVE-2026-21921
Reported by juniper · Published January 15, 2026
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.
Fixed versions
Upgrade to a fixed version or later. Language registries are listed first, then Linux distributions, then vendor products.
| Package | Ecosystem | Fixed in |
|---|---|---|
| junos_os_evolved | juniper | 22.4 |
| Junos OS | Juniper Networks | 23.4R2, 23.2R2-S5, 22.4R3-S8 |
| junos | juniper | 22.4 |
| Junos OS Evolved | Juniper Networks | 23.4R2-EVO, 23.2R2-S5-EVO, 22.4R3-S8-EVO |
Risk scores
Affected products
| Vendor | Product | Versions |
|---|---|---|
| Juniper Networks | Junos OS | 0, 23.2, 23.4 |
| Juniper Networks | Junos OS Evolved | 0, 23.2, 23.4 |
| Juniper Networks | Junos OS | 0, 23.2, 23.4 |
| Juniper Networks | Junos OS Evolved | 0, 23.2, 23.4 |
Timeline
- Jan 14, 2026 CVE Published
- Jan 15, 2026 PoC Published
- Jan 15, 2026 CVE Updated
- Jan 16, 2026 EPSS Score (30 in total, the first dated here)
- Mar 17, 2026 Security Advisory (3 in total, the first dated here)
- Mar 22, 2026 Coalition ESS Score (2 in total, the first dated here)
Query this with the API
The same record, from the CLI:
vulnetix vdb vuln CVE-2026-21921
vulnetix vdb fixes CVE-2026-21921Or with curl, using the org id and key from your account page:
curl -s -H "Authorization: ApiKey ${VULNETIX_ORG_ID}:${VULNETIX_API_KEY}" \
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