Junos OS (SRX firewalls)
CVE-2026-21910: EX4k Series, QFX5k Series: In an EVPN-VXLAN configuration link flaps cause Inter-VNI traffic drop
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).
Published
Automatic summary from the vendor's CVE record. We haven't written a full analysis of this vulnerability yet.
Affected and fixed versions
| Product / branch | Fixed in |
|---|---|
| Junos OS (EX4k Series, QFX5k Series) 0 | 21.4R3-S12 or later |
| Junos OS (EX4k Series, QFX5k Series) 22.2 | 22.2* or later |
| Junos OS (EX4k Series, QFX5k Series) 22.4 | 22.4R3-S8 or later |
| Junos OS (EX4k Series, QFX5k Series) 23.2 | 23.2R2-S5 or later |
| Junos OS (EX4k Series, QFX5k Series) 23.4 | 23.4R2-S5 or later |
| Junos OS (EX4k Series, QFX5k Series) 24.2 | 24.2R2-S3 or later |
| Junos OS (EX4k Series, QFX5k Series) 24.4 | 24.4R2 or later |
Always confirm against the vendor advisory, which lists every fixed hotfix.
What it is
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.
Am I affected?
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]
Workarounds
There are no known workarounds for this issue.
Exploitation
Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
Sources
KEV status, EPSS score and vendor data refreshed automatically, last on 13 Oct 2026.