CVE-2026-33774

OVERVIEW CVE-2026-33774 is an improper exception handling vulnerability in the packet forwarding engine of Juniper Networks Junos OS affecting MX Series routers. Specifically, firewall filters applied to non-zero loopback interfaces (lo0.n) fail to execute when those interfaces reside in the global or default routing instance, allowing unauthenticated network-based attackers to bypass configured firewall protections and reach the control plane. The vulnerability impacts MX platforms equipped with MPC10, MPC11, LC4800, LC9600 line cards, and MX304 devices running unpatched versions prior to specified thresholds across multiple release trains. SEVERITY The vulnerability carries a CVSS v3.1 score of 6.5 (MEDIUM) with a network-based attack vector requiring no authentication or user interaction, making exploitation straightforward from remote sources. The attack has low complexity and results in low confidentiality and integrity impacts without availability impact. While classified as MEDIUM severity, the nature of the vulnerability—direct firewall bypass leading to control plane access—carries meaningful operational risk for affected infrastructure. EXPLOITATION STATUS There is currently no evidence of active exploitation in the wild. The vulnerability does not appear on the CISA Known Exploited Vulnerabilities catalog, and no public exploit code has been disclosed. The EPSS score of 0.00036 indicates very low predicted exploitation probability. Community attention remains minimal, consistent with the low detection likelihood given the specific platform and configuration requirements necessary to be vulnerable.