Juniper Junos OS PFE EVPN-VXLAN DoS via Flapping Interface (before 24.4R2)
CVE-2026-21910 Published on January 15, 2026
Junos OS: 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).
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.
Vulnerability Analysis
Weakness Type
Improper Check for Unusual or Exceptional Conditions
The software does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the software.
Products Associated with CVE-2026-21910
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Affected Versions
Juniper Networks Junos OS:- Before 21.4R3-S12 is affected.
- Version 22.2 and below 22.2* is affected.
- Version 22.4 and below 22.4R3-S8 is affected.
- Version 23.2 and below 23.2R2-S5 is affected.
- Version 23.4 and below 23.4R2-S5 is affected.
- Version 24.2 and below 24.2R2-S3 is affected.
- Version 24.4 and below 24.4R2 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.