CVE-2026-21910

Summary

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.

Affected Software

VendorProductVersion RangeStatus
Juniper NetworksJunos OS0 < 21.4R3-S12affected
Juniper NetworksJunos OS22.2 < 22.2*affected
Juniper NetworksJunos OS22.4 < 22.4R3-S8affected
Juniper NetworksJunos OS23.2 < 23.2R2-S5affected
Juniper NetworksJunos OS23.4 < 23.4R2-S5affected
Juniper NetworksJunos OS24.2 < 24.2R2-S3affected
Juniper NetworksJunos OS24.4 < 24.4R2affected

Weaknesses

  • CWE-754: CWE-754 Improper Check for Unusual or Exceptional Conditions

Workarounds

There are no known workarounds for this issue.

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References