CVE-2026-102077: CWE-754 Improper Check for Unusual or Exceptional Conditions in Juniper Networks Junos OS

This vulnerability (CVE-2026-102077) arises from an improper check for unusual or exceptional conditions (CWE-754) in the Packet Forwarding Engine of Junos OS on MX Series with SPC3 line-cards. When a specific malformed IPv6 packet is received on devices with source NAT configured, the packet is not dropped as expected. Instead, a session is created and NAT resources are allocated. Repeated receipt of such packets leads to exhaustion of sessions or NAT resources, causing a denial-of-service condition that impacts all traffic through the device. Recovery requires rebooting the affected device. The vulnerability affects all Junos OS versions before 23.2R2-S4, versions 23.4 up to but not including 23.4R2-S5, and versions 24.2 up to but not including 24.2R2.

An unauthenticated, network-based attacker can exploit this vulnerability to cause a denial-of-service by exhausting session or NAT resources on affected Junos OS devices. This results in disruption of all traffic through the device until it is rebooted. There is no impact on confidentiality or integrity reported.

A fix is available in Junos OS versions 23.2R2-S4, 23.4R2-S5, and 24.2R2. Users should upgrade to these or later versions to remediate the vulnerability. Until patched, monitoring session usage (via 'show services sessions summary') and NAT pool usage (via 'show services nat pool') can help detect potential exploitation attempts. No vendor advisory content contradicts these recommendations.