An Improper Check for Unusual or Exceptional Conditions vulnerability in the kernel of Juniper Network Junos OS on MX Series allows a network based attacker with low privileges to cause a denial of service.

If a scaled configuration for Source class usage (SCU) / destination class usage (DCU) (more than 10 route classes) is present and the SCU/DCU statistics are gathered by executing specific SNMP requests or CLI commands, a 'vmcore' for the RE kernel will be seen which leads to a device restart. Continued exploitation of this issue will lead to a sustained DoS.

This issue only affects MX Series devices with MPC10, MPC11 or LC9600, and MX304. No other MX Series devices are affected.

This issue affects Juniper Networks Junos OS:

• All versions earlier than 20.4R3-S9;
• 21.2 versions earlier than 21.2R3-S6;
• 21.3 versions earlier than 21.3R3-S5;
• 21.4 versions earlier than 21.4R3;
• 22.1 versions earlier than 22.1R3;
• 22.2 versions earlier than 22.2R2;
• 22.3 versions earlier than 22.3R2.

To be exposed to this issue a scaled SCU/DCU configuration with more than 10 classes needs to be present on the device:

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-2024-21603.

The following software releases have been updated to resolve this specific issue: 20.4R3-S9, 21.2R3-S6, 21.3R3-S5, 21.4R3, 22.1R3, 22.2R2, 22.3R2, 22.4R1, and all subsequent releases.

This issue is being tracked as PR 1670797 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).

2024-01-10: 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-2024-21603 at cve.mitre.org