An improper interpretation conflict of certain data between certain software components within the Juniper Networks Junos OS devices does not allow certain traffic to pass through the device upon receipt from an ingress interface filtering certain specific types of traffic which is then being redirected to an egress interface on a different VLAN. This causes a Denial of Service (DoS) to those clients sending these particular types of traffic. Such traffic being sent by a client may appear genuine, but is non-standard in nature and should be considered as potentially malicious, and can be targeted to the device, or destined through it for the issue to occur.

This issues affects IPv4 and IPv6 traffic.

An indicator of compromise may be found by checking log files. You may find that traffic on the input interface has 100% of traffic flowing into the device, yet the egress interface shows 0 pps leaving the device.

For example:

Output between two interfaces would reveal something similar to:

Ingress, first interface:

Egress, second interface:

Dropped packets will not show up in DDoS monitoring/protection counters as issue is not caused by anti-DDoS protection mechanisms.

This issue affects:

Juniper Networks Junos OS:

• 17.3 versions prior to 17.3R3-S7 on NFX250, QFX5K Series, EX4600;
• 17.4 versions prior to 17.4R2-S11, 17.4R3-S3 on NFX250, QFX5K Series, EX4600;
• 18.1 versions prior to 18.1R3-S9 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4600;
• 18.2 versions prior to 18.2R3-S3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600;
• 18.3 versions prior to 18.3R3-S1 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series;
• 18.4 versions prior to 18.4R1-S5, 18.4R2-S3, 18.4R3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series;
• 19.1 versions prior to 19.1R1-S5, 19.1R2-S1, 19.1R3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series;
• 19.2 versions prior to 19.2R1-S5, 19.2R2 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series;
• 19.3 versions prior to 19.3R2-S3, 19.3R3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series;
• 19.4 versions prior to 19.4R1-S2, 19.4R2 on NFX250, NFX350, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series.

This issue does not affect Junos OS releases prior to 17.2R2.

The following minimal configuration is required on two interfaces passing traffic on different vlans between each other:

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-2021-0207 .

The following software releases have been updated to resolve this specific issue: 17.3R3-S7, 17.4R2-S11, 17.4R3-S3, 18.1R3-S9, 18.2R3-S3, 18.3R3-S1, 18.4R1-S5, 18.4R2-S3, 18.4R3, 19.1R1-S5, 19.1R2-S1, 19.1R3, 19.2R1-S5, 19.2R2, 19.3R2-S3, 19.3R3, 19.4R1-S2, 19.4R2, 20.1R1 and all subsequent releases.

This issue is being tracked as  1429543 .

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

• 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-2021-0207 at cve.mitre.org