How severe is CVE-2026-21921?

CVE-2026-21921 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-21921 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (25th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21921?

CVE-2026-21921 primarily affects Juniper Junos. In total, 58 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-21921?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-21921 have an EU (EUVD) identifier?

Yes. CVE-2026-21921 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-2693.

When was CVE-2026-21921 published?

CVE-2026-21921 was published on 2026-01-15 and last updated on 2026-06-17.

CVE-2026-21921

CVE-2026-21921 is a medium-severity vulnerability in Juniper Junos with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-416.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
CVSS v4: 7.1
EPSS exploit prediction: 0% (25th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-2693
Weakness: CWE-416
Affected product: Juniper Junos
Published: 2026-01-15
Last modified: 2026-06-17

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 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.

Frequently asked questions

What is 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.
How severe is CVE-2026-21921?: CVE-2026-21921 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-21921 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (25th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21921?: CVE-2026-21921 primarily affects Juniper Junos. In total, 58 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-21921?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-21921 have an EU (EUVD) identifier?: Yes. CVE-2026-21921 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-2693.
When was CVE-2026-21921 published?: CVE-2026-21921 was published on 2026-01-15 and last updated on 2026-06-17.

References

Affected products (58)

cpe:2.3:o:juniper:junos:*:*:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:-:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r1-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r1-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r2-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r2-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r3:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r3-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r3-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r3-s3:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r3-s4:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r3-s5:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r3-s6:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:22.4:r3-s7:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.2:-:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.2:r1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.2:r1-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.2:r1-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.2:r2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.2:r2-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.2:r2-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.2:r2-s3:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.2:r2-s4:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:-:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r1-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r1-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:*:*:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:22.4:-:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:22.4:r1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:22.4:r1-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:22.4:r1-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:22.4:r2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:22.4:r2-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:22.4:r2-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:22.4:r3:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:22.4:r3-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos_os_evolved:22.4:r3-s2:*:*:*:*:*:*

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