High [CVE-2026-102077] Improper Check for Unusual or Exceptional Conditions vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on MX Series with SPC3 allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS)

An Improper Check for Unusual or Exceptional Conditions vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on MX Series with SPC3 allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).

On MX Series with SPC3 line-card and source NAT configuration, when a specific malformed IPv6 packet is received, it is not dropped but instead a session is created and NAT resources are allocated. Continued receipt of such packets will eventually lead to session or resource exhaustion, which will impact all traffic through the device.

To recover the device needs to be rebooted. To monitor session usage, use the following:

show services sessions summary

show services nat pool

This issue affects Junos OS on MX Series with SPC3:

• All versions before 23.2R2-S4;
• 23.4 versions before 23.4R2-S5;