An Improper Check for Unusual or Exceptional Conditions (CWE-754) vulnerability exists in the packet forwarding engine of Juniper Networks Junos OS on MX Series devices with MPC10/11, LC4800/9600/4802, and MX304 hardware. This flaw allows adjacent subscribers to bypass ingress firewall filters configured on static interfaces, meaning that neither protocol-level filtering nor upstream bandwidth limitations are enforced. Affected versions include 23.2R2-S1 through versions before 23.2R2-S7, 23.4R2 through before 23.4R2-S7, and versions before 24.2R2-S3, 24.4R2-S2, and 25.2R2. The vulnerability has a CVSS 3.1 base score of 4.7, indicating medium severity. Juniper manages remediation for this cloud-hosted service, and a patch is available.

Ingress firewall filters on affected Junos OS MX Series devices are bypassed for adjacent subscribers, disabling protocol-level filtering and upstream bandwidth limitations. This could allow unauthorized traffic to pass through firewall filters, potentially leading to policy violations or network misuse. There is no impact on confidentiality or availability reported, only integrity is affected. No known exploits in the wild have been reported.

A patch is available for this vulnerability. Since this is a cloud-hosted service, Juniper Networks manages remediation server-side. Users should verify with Juniper's official advisory to confirm patch deployment status and ensure their devices are updated to fixed versions. No additional mitigation actions are indicated by the vendor advisory.