An Improper Check for Unusual or Exceptional Conditions flaw in the packet forwarding engine of Juniper Networks Junos OS allows an unauthenticated network‑adjacent attacker to cause traffic between VXLAN Network Identifiers to drop with a simple interface flap. The resulting denial of service interrupts inter‑VNI communication, impacting network availability on affected chassis. This vulnerability is captured by CWE‑754, which denotes failure to validate exceptional conditions during forwarding logic.

The flaw targets Juniper Networks Junos OS on EX4k Series and QFX5k Series platforms, specifically the QFX5110, QFX5120, QFX5200, EX4100, EX4300, EX4400, and EX4650 devices. All software versions before 21.4R3‑S12, the entirety of 22.2, versions of 22.4 up to 22.4R3‑S8, versions of 23.2 up to 23.2R2‑S5, versions of 23.4 up to 23.4R2‑S5, versions of 24.2 up to 24.2R2‑S3, and versions of 24.4 up to 24.4R2 are impacted.

The CVSS score of 7.1 indicates medium‑to‑high severity, but the EPSS score of less than 1% suggests a presently low exploitation probability. The vulnerability is not listed in the CISA KEV catalog. An unauthenticated network‑adjacent attacker can trigger the issue by flapping an interface without privileged credentials, leading to a denial of service. The vulnerability can be neutralised by restarting the affected Fabric Processing Card, but permanent mitigation requires upgrading to a release that contains the fix.