CVE-2026-21910

CVE-2026-21910 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-754.

Key facts

Description

An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (PFE) of Juniper Networks Junos OS on EX4k Series and QFX5k Series platforms allows an unauthenticated network-adjacent attacker flapping an interface to cause traffic between VXLAN Network Identifiers (VNIs) to drop, leading to a Denial of Service (DoS). On all EX4k and QFX5k platforms, a link flap in an EVPN-VXLAN configuration Link Aggregation Group (LAG) results in Inter-VNI traffic dropping when there are multiple load-balanced next-hop routes for the same destination. This issue is only applicable to systems that support EVPN-VXLAN Virtual Port-Link Aggregation Groups (VPLAG), such as the QFX5110, QFX5120, QFX5200, EX4100, EX4300, EX4400, and EX4650. Service can only be restored by restarting the affected FPC via the 'request chassis fpc restart slot <slot-number>' command. This issue affects Junos OS on EX4k and QFX5k Series:  * all versions before 21.4R3-S12,  * all versions of 22.2 * from 22.4 before 22.4R3-S8,  * from 23.2 before 23.2R2-S5,  * from 23.4 before 23.4R2-S5,  * from 24.2 before 24.2R2-S3, * from 24.4 before 24.4R2.

Frequently asked questions

What is CVE-2026-21910?
An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (PFE) of Juniper Networks Junos OS on EX4k Series and QFX5k Series platforms allows an unauthenticated network-adjacent attacker flapping an interface to cause traffic between VXLAN Network Identifiers (VNIs) to drop, leading to a Denial of Service (DoS). On all EX4k and QFX5k platforms, a link flap in an EVPN-VXLAN configuration Link Aggregation Group (LAG) results in Inter-VNI traffic dropping when there are multiple load-balanced next-hop routes for the same destination. This issue is only applicable to systems that support EVPN-VXLAN Virtual Port-Link Aggregation Groups (VPLAG), such as the QFX5110, QFX5120, QFX5200, EX4100, EX4300, EX4400, and EX4650. Service can only be restored by restarting the affected FPC via the 'request chassis fpc restart slot <slot-number>' command. This issue affects Junos OS on EX4k and QFX5k Series:  * all versions before 21.4R3-S12,  * all versions of 22.2 * from 22.4 before 22.4R3-S8,  * from 23.2 before 23.2R2-S5,  * from 23.4 before 23.4R2-S5,  * from 24.2 before 24.2R2-S3, * from 24.4 before 24.4R2.
How severe is CVE-2026-21910?
CVE-2026-21910 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-21910 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (16th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21910?
CVE-2026-21910 primarily affects Juniper Junos. In total, 65 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-21910?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-21910 have an EU (EUVD) identifier?
Yes. CVE-2026-21910 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-2694.
When was CVE-2026-21910 published?
CVE-2026-21910 was published on 2026-01-15 and last updated on 2026-06-17.

References

Affected products (65)

More vulnerabilities in Juniper Junos

All CVEs affecting Juniper Junos →

Other CWE-754 (Improper Check for Unusual or Exceptional Conditions) vulnerabilities

Browse all CWE-754 (Improper Check for Unusual or Exceptional Conditions) vulnerabilities →