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.

This issue requires the following configuration:

[interfaces <if> ether-options 802.3ad ae0]
[interfaces ae0 aggregated-ether-options lacp]

[protocols bgp group <name> family evpn signaling]
[protocols evpn encapsulation vxlan]

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was seen during production usage.

The following software releases have been updated to resolve this specific issue: Junos OS 21.4R3-S12, 22.4R3-S8, 23.2R2-S5, 23.4R2-S5, 24.2R2-S3, 24.4R2, 25.2R1, and all subsequent releases.

This issue is being tracked as 1847849 which is visible on the Customer Support website.

Note: Juniper SIRT's policy is not to evaluate releases which are beyond End of Engineering (EOE) or End of Life (EOL).

There are no known workarounds for this issue.

2026-01-14: Initial Publication

• KB16613: Overview of the Juniper Networks SIRT Quarterly Security Bulletin Publication Process [juniper.net]
• KB16765: In which releases are vulnerabilities fixed? [juniper.net]
• KB16446: Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories [juniper.net]
• Report a Security Vulnerability - How to Contact the Juniper Networks Security Incident Response Team