An always-incorrect control flow implementation in the implicit filter terms of Juniper Networks Junos OS and Junos OS Evolved on ACX5800, EX9200 Series, MX10000 Series, MX240, MX480, MX960 devices with affected Trio line cards allows an attacker to exploit an interdependency in the PFE UCODE microcode of the Trio chipset with various line cards to cause packets destined to the devices interfaces to cause a Denial of Service (DoS) condition by looping the packet with an unreachable exit condition ('Infinite Loop'). To break this loop once it begins one side of the affected LT interfaces will need to be disabled. Once disabled, the condition will clear and the disabled LT interface can be reenabled.

Continued receipt and processing of these packets will create a sustained Denial of Service (DoS) condition.

This issue only affects LT-LT interfaces. Any other interfaces are not affected by this issue.

This issue affects the following cards:

An Indicator of Compromise (IoC) can be seen by examining the traffic of the LT-LT interfaces for excessive traffic using the following command:

Before loop impact:

After loop impact:

This issue affects:

Juniper Networks Junos OS on ACX5800, EX9200 Series, MX10000 Series, MX240, MX480, MX960.

• Versions 15.1F6, 16.1R1, and later versions prior to 16.1R7-S8;
• 17.1 versions prior to 17.1R2-S12;
• 17.2 versions prior to 17.2R3-S4;
• 17.3 versions prior to 17.3R3-S8;
• 17.4 versions prior to 17.4R2-S10, 17.4R3-S2;
• 18.1 versions prior to 18.1R3-S10;
• 18.2 versions prior to 18.2R2-S7, 18.2R3-S3;
• 18.3 versions prior to 18.3R1-S7, 18.3R3-S2;
• 18.4 versions prior to 18.4R1-S7, 18.4R2-S4, 18.4R3-S2;
• 19.1 versions prior to 19.1R1-S5, 19.1R2-S1, 19.1R3;
• 19.2 versions prior to 19.2R1-S4, 19.2R2;
• 19.3 versions prior to 19.3R2-S3, 19.3R3;
• 19.4 versions prior to 19.4R1-S1, 19.4R2.

This issue does not affect the MX10001.

• This issue does not affect Juniper Networks Junos OS versions prior to 15.1F6, 16.1R1.

Juniper Networks Junos OS Evolved on ACX5800, EX9200 Series, MX10000 Series, MX240, MX480, MX960

19.4 versions prior to 19.4R2-EVO.

This issue does not affect the MX10001.

An example of an affected configuration is one where a Trio chipset line card is in use with a logical-tunnel interface set up to communicate to a second logical tunnel (LT-to-LT) interface.

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-2021-0273 .

The following software releases have been updated to resolve this specific issue:

Junos OS: 16.1R7-S8, 17.1R2-S12, 17.2R3-S4, 17.3R3-S8, 17.4R2-S10, 17.4R3-S2, 18.1R3-S10, 18.2R2-S7, 18.2R3-S3, 18.3R1-S7, 18.3R3-S2, 18.4R1-S7, 18.4R2-S4, 18.4R3-S2, 19.1R1-S5, 19.1R2-S1, 19.1R3, 19.2R1-S4, 19.2R2, 19.3R2-S3, 19.3R3, 19.4R1-S1, 19.4R2, 20.1R1, and all subsequent releases.

Junos OS Evolved: 19.4R2-EVO, 20.1R1-EVO, and all subsequent releases.

This issue is being tracked as  1478759 .

Software releases or updates are available for download at https://support.juniper.net/support/downloads/

2021-04-14: Initial Publication.

• 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
• CVE-2021-0273 at cve.mitre.org