Juniper Junos OS up to 24.4R1 Packet Forwarding Engine unusual condition

Summaryinfo

A vulnerability classified as critical was found in Juniper Junos OS up to 24.4R1. This impacts an unknown function of the component Packet Forwarding Engine. The manipulation results in unusual condition. This vulnerability is known as CVE-2026-21910. Access to the local network is required for this attack. No exploit is available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability classified as critical has been found in Juniper Junos OS up to 24.4R1. Affected is an unknown function of the component Packet Forwarding Engine. The manipulation with an unknown input leads to a unusual condition vulnerability. CWE is classifying the issue as CWE-754. The product 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 product. This is going to have an impact on availability. CVE summarizes:

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.

The advisory is shared for download at supportportal.juniper.net. This vulnerability is traded as CVE-2026-21910 since 01/05/2026. The exploitability is told to be easy. The attack needs to approached within the local network. The exploitation doesn't require any form of authentication. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 01/17/2026).

Upgrading to version 21.4R3-S12, 22.2*, 22.4R3-S8, 23.2R2-S5, 23.4R2-S5, 24.2R2-S3 or 24.4R2 eliminates this vulnerability.

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Productinfo

Type

• Router Operating System

Vendor

• Juniper

Name

• Junos OS

Version

• 21.4R3-S11
• 22.4R3-S7
• 23.2R2-S4
• 23.4R2-S4
• 24.2R2-S2
• 24.4R1

License

• commercial

Website

• Vendor: https://www.juniper.net/

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