Improper Check for Exceptional Conditions Vulnerability in Juniper Networks Junos OS on MX Series

CVE-2026-33774

What is CVE-2026-33774?

An improper check vulnerability has been identified in the packet forwarding engine of Juniper Networks' Junos OS on MX Series devices. This weakness allows an unauthenticated network-based attacker to bypass configured firewall filters and directly access the device's control plane. Specifically, when using MPC10, MPC11, LC4800, or LC9600 line cards, firewall filters linked to non-zero loopback interfaces may not execute as intended if those interfaces are configured in the global VRF or default routing instance. This misconfiguration can lead to significant security implications as critical access controls are rendered ineffective.

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