A Protection Mechanism Failure vulnerability in kernel filter processing of Juniper Networks Junos OS allows an attacker sending IPv6 traffic destined to the device to effectively bypass any firewall filtering configured on the interface.

Due to an issue with Junos OS kernel filter processing, the 'payload-protocol' match is not being supported, causing any term containing it to accept all packets without taking any other action. In essence, these firewall filter terms were being processed as an 'accept' for all traffic on the interface destined for the control plane, even when used in combination with other match criteria.

This issue only affects firewall filters protecting the device's control plane. Transit firewall filtering is unaffected by this vulnerability.

This issue affects Junos OS: 

• all versions before 21.2R3-S9, 
• from 21.4 before 21.4R3-S11, 
• from 22.2 before 22.2R3-S7, 
• from 22.4 before 22.4R3-S7, 
• from 23.2 before 23.2R2-S4, 
• from 23.4 before 23.4R2-S5, 
• from 24.2 before 24.2R2-S1, 
• from 24.4 before 24.4R1-S2, 24.4R2.

The following firewall filter configuration, using payload-protocol, will fail to match, allowing traffic to be accepted rather than discarded:

[firewall family inet6 filter example-filter term reject-tcp from payload-protocol tcp]
[firewall family inet6 filter example-filter term reject-tcp then discard]
[firewall family inet6 filter example-filter term allow-rest then accept]

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was seen during production usage.

The following software releases have been updated to resolve this specific issue: 21.2R3-S9, 21.4R3-S11, 22.2R3-S7, 22.4R3-S7, 23.2R2-S4, 23.4R2-S5, 24.2R2-S1, 24.4R1-S2, 24.4R2, 25.2R1, and all subsequent releases.

This issue is being tracked as 1844796 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).

Utilize 'next-header' match instead of 'payload-protocol' in any firewall filter configurations.

2025-07-09: Initial Publication
2025-07-15: Clarified that only traffic destined to the control plane is affected

• KB16613: Overview of the Juniper Networks SIRT Quarterly Security Bulletin Publication Process [juniper.net]
• KB16765: In which releases are vulnerabilities fixed? [juniper.net]
• KB16446: Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories [juniper.net]
• Report a Security Vulnerability - How to Contact the Juniper Networks Security Incident Response Team
• https://www.cve.org/CVERecord?id=CVE-2025-52951