CVE-2026-21906

Summary

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.

Affected Software

VendorProductVersion RangeStatus
Juniper NetworksJunos OS0 < 21.4R3-S12affected
Juniper NetworksJunos OS22.4 < 22.4R3-S8affected
Juniper NetworksJunos OS23.2 < 23.2R2-S5affected
Juniper NetworksJunos OS23.4 < 23.4R2-S5affected
Juniper NetworksJunos OS24.2 < 24.2R2-S3affected
Juniper NetworksJunos OS24.4 < 24.4R2-S1affected
Juniper NetworksJunos OS25.2 < 25.2R1-S1, 25.2R2affected

Weaknesses

  • CWE-755: CWE-755 Improper Handling of Exceptional Conditions

Workarounds

  • Disable GRE performance acceleration via 'deactivate security flow gre-performance-acceleration' or
  • Disable PMI:via 'set security flow power-mode-disable'

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: yes
    • Technical Impact: partial

References