Juniper Junos OS up to 25.2R1-S1 on SRX Packet Forwarding Engine exceptional condition

Summaryinfo

A vulnerability marked as critical has been reported in Juniper Junos OS up to 25.2R1-S1 on SRX. This vulnerability affects unknown code of the component Packet Forwarding Engine. This manipulation causes exceptional condition. This vulnerability appears as CVE-2026-21906. The attack may be initiated remotely. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical was found in Juniper Junos OS up to 25.2R1-S1 on SRX. Affected by this vulnerability is an unknown code of the component Packet Forwarding Engine. The manipulation with an unknown input leads to a exceptional condition vulnerability. The CWE definition for the vulnerability is CWE-755. The product does not handle or incorrectly handles an exceptional condition. As an impact it is known to affect availability. The summary by CVE is:

An Improper Handling of Exceptional Conditions vulnerability in the packet forwarding engine (PFE) of Juniper Networks Junos OS on SRX Series allows an unauthenticated network-based attacker sending a specific ICMP packet through a GRE tunnel to cause the PFE to crash and restart. When PowerMode IPsec (PMI) and GRE performance acceleration are enabled and the device receives a specific ICMP packet, a crash occurs in the SRX PFE, resulting in traffic loss. PMI is enabled by default, and GRE performance acceleration can be enabled by running the configuration command shown below. PMI is a mode of operation that provides IPsec performance improvements using Vector Packet Processing. Note that PMI with GRE performance acceleration is only supported on specific SRX platforms. This issue affects Junos OS on the SRX Series: * all versions before 21.4R3-S12,  * 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-S1,  * from 25.2 before 25.2R1-S1, 25.2R2.

It is possible to read the advisory at supportportal.juniper.net. This vulnerability is known as CVE-2026-21906 since 01/05/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 01/16/2026).

Upgrading to version 21.4R3-S12, 22.4R3-S8, 23.2R2-S5, 23.4R2-S5, 24.2R2-S3, 24.4R2-S1, 25.2R1-S1 or 25.2R2 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
• 24.4R2-S0
• 25.2R1
• 25.2R1-S1

License

• commercial

Website

• Vendor: https://www.juniper.net/

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