CVE-2026-21906

/// Technical description

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 24.2

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References