CVSS: v3.1: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)CVSS: v4.0: 8.7 (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:U/RE:M)
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
To monitor source NAT resource usage, use the following: show services nat pool
This issue affects Junos OS on MX Series with SPC3:
To be exposed to this issue, you need to have source NAT configured similar to the following:
[ services nat source rule-set <rule set name> rule <name> then source-nat ... ]Juniper SIRT is not aware of any malicious exploitation of this vulnerability.This issue was seen during production usage.This issue has been assigned CVE-2026-102077.
[ services nat source rule-set <rule set name> rule <name> then source-nat ... ]
The following software releases have been updated to resolve this specific issue: Junos OS: 23.2R2-S4, 23.4R2-S5, 24.2R2, 24.4R1, and all subsequent releases.This issue is being tracked as 1803056 which is visible on the Customer Support website.Note: Juniper SIRT's policy is not to evaluate releases which are beyond End of Engineering (EOE) or End of Life (EOL).
There are no known workarounds for this issue.
2026-10-14: Initial Publication