CVE-2026-21910 - Junos OS Plugin
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 ' 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.
CVE-2026-21910
HIGH
CVSS 7.1
Published 2026-01-15
Updated 2026-02-25
AI Risk Elevated (71/100)
Active Exploit: No strong signal
Published Exploit: No public exploit references
Priority: P3 Priority
Severity Band
HIGH
CVSS Vector
CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:U/V:X/RE:M/U:Green
Affected Components
1
Reference Links
2
AI Risk Engine
Elevated (71/100)
Exploitability
Medium
Active Exploitation
No strong signal
Published Exploit Status
No public exploit references
AI Context
Machine-generated threat intelligence
AI
Updated 10 days ago
AI enriched 10 days ago (2026-04-09 08:01 UTC)
Technical 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…
Potential Impact
Severity is HIGH (CVSS 7.1). Depending on deployment context, affected components may be exposed to unauthorized actions or data integrity risk.
Exploitability Assessment
Exploitability is assessed as Medium based on low-bar exploit prerequisites.
Primary risk drivers: low-bar exploit prerequisites
Mitigation Recommendations
Validate affected product versions, prioritize patching, and monitor references for vendor remediation guidance. If immediate patching is not possible, apply compensating controls and limit exposure of vulnerable surfaces.
Detection & Monitoring
Track authentication anomalies, unexpected file writes, and suspicious plugin API activity around affected components.
Business Impact Lens
Prioritize remediation where affected components process customer data, admin sessions, or Internet-exposed workflows.
