Vulnerability Database

328,409

Total vulnerabilities in the database

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 <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.
  • Published: Jan 15, 2026
  • Updated: Jan 16, 2026
  • CVE: CVE-2026-21910
  • Severity: Medium
  • Exploit:

CVSS v3:

  • Severity: Medium
  • Score: 6.5
  • AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWEs:

Software From Fixed in
juniper / junos - 21.4
juniper / junos 21.4 21.4.x
juniper / junos 21.4-r1 21.4-r1.x
juniper / junos 21.4-r1-s1 21.4-r1-s1.x
juniper / junos 21.4-r1-s2 21.4-r1-s2.x
juniper / junos 21.4-r2 21.4-r2.x
juniper / junos 21.4-r2-s1 21.4-r2-s1.x
juniper / junos 21.4-r2-s2 21.4-r2-s2.x
juniper / junos 21.4-r3 21.4-r3.x
juniper / junos 21.4-r3-s1 21.4-r3-s1.x
juniper / junos 21.4-r3-s10 21.4-r3-s10.x
juniper / junos 21.4-r3-s11 21.4-r3-s11.x
juniper / junos 21.4-r3-s2 21.4-r3-s2.x
juniper / junos 21.4-r3-s3 21.4-r3-s3.x
juniper / junos 21.4-r3-s4 21.4-r3-s4.x
juniper / junos 21.4-r3-s5 21.4-r3-s5.x
juniper / junos 21.4-r3-s6 21.4-r3-s6.x
juniper / junos 21.4-r3-s7 21.4-r3-s7.x
juniper / junos 21.4-r3-s8 21.4-r3-s8.x
juniper / junos 21.4-r3-s9 21.4-r3-s9.x
juniper / junos 22.2 22.2.x
juniper / junos 22.4 22.4.x
juniper / junos 22.4-r1 22.4-r1.x
juniper / junos 22.4-r1-s1 22.4-r1-s1.x
juniper / junos 22.4-r1-s2 22.4-r1-s2.x
juniper / junos 22.4-r2 22.4-r2.x
juniper / junos 22.4-r2-s1 22.4-r2-s1.x
juniper / junos 22.4-r2-s2 22.4-r2-s2.x
juniper / junos 22.4-r3 22.4-r3.x
juniper / junos 22.4-r3-s1 22.4-r3-s1.x
juniper / junos 22.4-r3-s2 22.4-r3-s2.x
juniper / junos 22.4-r3-s3 22.4-r3-s3.x
juniper / junos 22.4-r3-s4 22.4-r3-s4.x
juniper / junos 22.4-r3-s5 22.4-r3-s5.x
juniper / junos 22.4-r3-s6 22.4-r3-s6.x
juniper / junos 22.4-r3-s7 22.4-r3-s7.x
juniper / junos 23.2 23.2.x
juniper / junos 23.2-r1 23.2-r1.x
juniper / junos 23.2-r1-s1 23.2-r1-s1.x
juniper / junos 23.2-r1-s2 23.2-r1-s2.x
juniper / junos 23.2-r2 23.2-r2.x
juniper / junos 23.2-r2-s1 23.2-r2-s1.x
juniper / junos 23.2-r2-s2 23.2-r2-s2.x
juniper / junos 23.2-r2-s3 23.2-r2-s3.x
juniper / junos 23.2-r2-s4 23.2-r2-s4.x
juniper / junos 23.4 23.4.x
juniper / junos 23.4-r1 23.4-r1.x
juniper / junos 23.4-r1-s1 23.4-r1-s1.x
juniper / junos 23.4-r1-s2 23.4-r1-s2.x
juniper / junos 23.4-r2 23.4-r2.x
juniper / junos 23.4-r2-s1 23.4-r2-s1.x
juniper / junos 23.4-r2-s2 23.4-r2-s2.x
juniper / junos 23.4-r2-s3 23.4-r2-s3.x
juniper / junos 23.4-r2-s4 23.4-r2-s4.x
juniper / junos 24.2 24.2.x
juniper / junos 24.2-r1 24.2-r1.x
juniper / junos 24.2-r1-s1 24.2-r1-s1.x
juniper / junos 24.2-r1-s2 24.2-r1-s2.x
juniper / junos 24.2-r2 24.2-r2.x
juniper / junos 24.2-r2-s1 24.2-r2-s1.x
juniper / junos 24.2-r2-s2 24.2-r2-s2.x
juniper / junos 24.4 24.4.x
juniper / junos 24.4-r1 24.4-r1.x
juniper / junos 24.4-r1-s2 24.4-r1-s2.x
juniper / junos 24.4-r1-s3 24.4-r1-s3.x

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.