This vulnerability (CVE-2026-57020) involves an improper check for unusual or exceptional conditions (CWE-754) in the packet forwarding engine of Junos OS on QFX10000 Series devices. When IPv6 multicast packets reach a non-IRB interface of a spine switch in an EVPN-VxLAN environment, the packets are flooded endlessly to other spine and ESI leaf switches, causing link saturation and denial of service. The vulnerability affects all versions before 23.2R2-S7, 23.4 versions before 23.4R2-S8, 24.2 versions before 24.2R2-S4, and 24.4 versions before 24.4R2-S4. Junos versions after 24.4 do not support QFX10000 devices and are not affected.

An unauthenticated, adjacent attacker can trigger a denial-of-service condition by sending IPv6 multicast traffic that causes packet flooding in an endless loop across spine and leaf switches. This results in saturation of network links and disruption of legitimate traffic on affected QFX10000 Series devices running vulnerable Junos OS versions. There is no impact on confidentiality or integrity, only availability is affected.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The vulnerability affects specific Junos OS versions prior to 23.2R2-S7, 23.4R2-S8, 24.2R2-S4, and 24.4R2-S4. Users should upgrade to these fixed versions or later where support for QFX10000 is maintained. For versions after 24.4, QFX10000 devices are not supported and thus not affected. Monitor Juniper Networks advisories for official fixes and recommended actions.