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MEDIUM · 6.5

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 unauthentic...

Vulnerability 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.

CVSS Score

6.5

MEDIUM

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack Vector
ADJACENT_NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH

Affected Products

VendorProductVersions
JuniperJunos< 21.4
JuniperEx4000-
JuniperEx4100-
JuniperEx4100-F-
JuniperEx4100-H-
JuniperEx4300-
JuniperEx4400-
JuniperEx4600-
JuniperEx4650-
JuniperQfx5110-
JuniperQfx5120-
JuniperQfx5130-
JuniperQfx5200-
JuniperQfx5210-
JuniperQfx5220-
JuniperQfx5230-64Cd-
JuniperQfx5240-
JuniperQfx5241-
JuniperQfx5700-

Related Weaknesses (CWE)

CWE-754

References

FAQ

What is CVE-2026-21910?

CVE-2026-21910 is a vulnerability with a CVSS score of 6.5 (MEDIUM). 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 unauthentic...

How severe is CVE-2026-21910?

CVE-2026-21910 has been rated MEDIUM with a CVSS base score of 6.5/10. Review the CVSS metrics above for detailed severity breakdown.

Is there a patch for CVE-2026-21910?

Check the references section above for vendor advisories and patch information. Affected products include: Juniper Junos, Juniper Ex4000, Juniper Ex4100, Juniper Ex4100-F, Juniper Ex4100-H.