A Race Condition (Concurrent Execution using Shared Resource with Improper Synchronization) vulnerability in the firewall process (dfwd) of Juniper Networks Junos OS allows an attacker to bypass the firewall rule sets applied to the input loopback filter on any interfaces of a device.

This issue is detectable by reviewing the PFE firewall rules, as well as the firewall counters and seeing if they are incrementing or not.

For example:

This issue affects:

Juniper Networks Junos OS:

• 14.1X53 versions prior to 14.1X53-D53 on QFX Series;
• 14.1 versions 14.1R1 and later versions prior to 15.1 versions prior to 15.1R7-S6 on QFX Series, PTX Series;
• 15.1X53 versions prior to 15.1X53-D593 on QFX Series;
• 16.1 versions prior to 16.1R7-S7 on QFX Series, PTX Series;
• 16.2 versions prior to 16.2R2-S11, 16.2R3 on QFX Series, PTX Series;
• 17.1 versions prior to 17.1R2-S11, 17.1R3-S2 on QFX Series, PTX Series;
• 17.2 versions prior to 17.2R1-S9, 17.2R3-S3 on QFX Series, PTX Series;
• 17.3 versions prior to 17.3R2-S5, 17.3R3-S7 on QFX Series, PTX Series;
• 17.4 versions prior to 17.4R2-S9, 17.4R3 on QFX Series, PTX Series;
• 18.1 versions prior to 18.1R3-S9 on QFX Series, PTX Series;
• 18.2 versions prior to 18.2R2-S6, 18.2R3-S3 on QFX Series, PTX Series;
• 18.3 versions prior to 18.3R1-S7, 18.3R2-S3, 18.3R3-S1 on QFX Series, PTX Series;
• 18.4 versions prior to 18.4R1-S5, 18.4R2-S3, 18.4R3 on QFX Series, PTX Series;
• 19.1 versions prior to 19.1R1-S4, 19.1R2-S1, 19.1R3 on QFX Series, PTX Series;
• 19.2 versions prior to 19.2R1-S3, 19.2R2 on QFX Series, PTX Series.

This issue impact all filters families (inet, inet6, etc.) yet only on input loopback filters.

It does not does not rely upon the location where a filter is set, impacting both logical and physical interfaces.

Configuration examples for input filtering are posted on the support site and in product documentation.

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-2021-0247 .

The following software releases have been updated to resolve this specific issue: Junos OS 14.1X53-D53, 15.1R7-S6, 15.1X53-D593, 16.1R7-S7, 16.2R2-S11, 16.2R3, 17.1R2-S11, 17.1R3-S2, 17.2R1-S9, 17.2R3-S3, 17.3R2-S5, 17.3R3-S7, 17.4R2-S9, 17.4R3, 18.1R3-S9, 18.2R2-S6, 18.2R3-S3, 18.3R1-S7, 18.3R2-S3, 18.3R3-S1, 18.4R1-S5, 18.4R2-S3, 18.4R3, 19.1R1-S4, 19.1R2-S1, 19.1R3, 19.2R1-S3, 19.2R2, 19.3R1, and all subsequent releases.

This issue is being tracked as  1430385 .

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

2021-04-14: Initial Publication.
2021-04-15: Removed spurious 18.4R2-S7 release entry in problem description.

• 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-2021-0247 at cve.mitre.org