A signal handler race condition exists in the Layer 2 Address Learning Daemon (L2ALD) of Juniper Networks Junos OS due to the absence of a specific protection mechanism to avoid a race condition which may allow an attacker to bypass the storm-control feature on devices. This issue is a corner case and only occurs during specific actions taken by an administrator of a device under certain specifics actions which triggers the event. The event occurs less frequently on devices which are not configured with Virtual Chassis configurations, and more frequently on devices configured in Virtual Chassis configurations. This issue is not specific to any particular Junos OS platform.

An Indicator of Compromise (IoC) may be seen by reviewing log files for the following error message seen by executing the following show statement:

Result to look for:

This issue affects:

Juniper Networks Junos OS:

• 14.1X53 versions prior to 14.1X53-D49 on EX Series;
• 15.1 versions prior to 15.1R7-S6;
• 15.1X49 versions prior to 15.1X49-D191, 15.1X49-D200 on SRX Series;
• 16.1 versions prior to 16.1R7-S7;
• 16.2 versions prior to 16.2R2-S11, 16.2R3;
• 17.1 versions prior to 17.1R2-S11, 17.1R3;
• 17.2 versions prior to 17.2R2-S8, 17.2R3-S3;
• 17.3 versions prior to 17.3R2-S5, 17.3R3-S7;
• 17.4 versions prior to 17.4R2-S9, 17.4R3;
• 18.1 versions prior to 18.1R3-S5;
• 18.2 versions prior to 18.2R2-S6, 18.2R3;
• 18.3 versions prior to 18.3R1-S7, 18.3R2-S3, 18.3R3;
• 18.4 versions prior to 18.4R1-S5, 18.4R2;
• 19.1 versions prior to 19.1R1-S4, 19.1R2.

Devices configured with storm control may be impacted. To review if a device is configured with storm control, refer to the command structure under:

Examples of of storm control configurations follow:

For Enhanced Layer 2 Software (ELS) release:

(see https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/rate-limiting-storm-control-disabling-cli-els.html for reference)

For non-ELS release:

or

(see https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/rate-limiting-storm-control-disabling-cli.html  for reference)

Refer to your specific product guides and the Junos OS Security Services Administration Guide for further information located at https://www.juniper.net/documentation/en_US/junos/information-products/pathway-pages/system-basics/security-services.html

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-2021-0244 .

The following software releases have been updated to resolve this specific issue: 14.1X53-D49, 15.1R7-S6, 15.1X49-D191, 15.1X49-D200, 15.1X53-D592, 16.1R7-S7, 16.1R8, 16.2R2-S11, 16.2R3, 17.1R2-S11, 17.1R3, 17.2R2-S8, 17.2R3-S3, 17.3R2-S5, 17.3R3-S7, 17.4R2-S9, 17.4R3, 18.1R3-S5, 18.2R2-S6, 18.2R3, 18.3R1-S7, 18.3R2-S3, 18.3R3, 18.4R1-S5, 18.4R2, 19.1R1-S4, 19.1R2, 19.2R1, and all subsequent releases.

This issue is being tracked as  1403424 .

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-2021-0244 at cve.mitre.org