Juniper Junos OS: 2026-01 Security Bulletin: Junos OS: EX4k Series, QFX5k Series: In an EVPN-VXLAN configuration link flaps cause Inter-VNI traffic drop (JSA106009) (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.