CVE-2026-21910

Inter-VNI traffic loss via LAG link flap

Published Jan 15, 2026 · Updated Jan 15, 2026

Denial of service in Junos OS on EX4k and QFX5k platforms allows attackers to drop inter-VNI traffic through an interface link flap. In an EVPN-VXLAN LAG, the PFE mishandles a link-flap state change when several load-balanced next hops share a destination, leaving inter-VNI forwarding unavailable. Exploitation requires unauthenticated, network-adjacent access to flap an interface on a VPLAG-capable system, and traffic remains unavailable until the affected FPC restarts.

CVSS severity7.1
High
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in Junos OS on EX4k and QFX5k platforms allows attackers to drop inter-VNI traffic through an interface link flap. In an EVPN-VXLAN LAG, the PFE mishandles a link-flap state change when several load-balanced next hops share a destination, leaving inter-VNI forwarding unavailable. Exploitation requires unauthenticated, network-adjacent access to flap an interface on a VPLAG-capable system, and traffic remains unavailable until the affected FPC restarts.

The record

CVE
CVE-2026-21910
Published
Jan 15, 2026
Updated
Jan 15, 2026
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-754
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 15, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 15, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <21.4R3-S12
  2. Affected versionversion=22.2 <22.2*
  3. Affected versionversion=22.4 <22.4R3-S8
  4. Affected versionversion=23.2 <23.2R2-S5
  5. Affected versionversion=23.4 <23.4R2-S5
  6. Affected versionversion=24.2 <24.2R2-S3
  7. Affected versionversion=24.4 <24.4R2

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=0 <21.4R3-S12; version=22.2 <22.2*; version=22.4 <22.4R3-S8; version=23.2 <23.2R2-S5; version=23.4 <23.4R2-S5; version=24.2 <24.2R2-S3; version=24.4 <24.4R2

Published CVSS scores

7.1Juniper Networks, Inc.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
6.5Juniper Networks, Inc.CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-754Improper Check for Unusual or Exceptional Conditions

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo