An Improper Input Validation vulnerability in J-Web of Juniper Networks Junos OS allows a locally authenticated J-Web attacker to escalate their privileges to root over the target device.

This issue affects:

Juniper Networks Junos OS

• All versions prior to 18.3R3-S5;
• 18.4 versions prior to 18.4R3-S9;
• 19.1 versions prior to 19.1R3-S6;
• 19.2 versions prior to 19.2R3-S3;
• 19.3 versions prior to 19.3R3-S3;
• 19.4 versions prior to 19.4R3-S5;
• 20.1 versions prior to 20.1R3-S1;
• 20.2 versions prior to 20.2R3-S2;
• 20.3 versions prior to 20.3R3-S1;
• 20.4 versions prior to 20.4R3;
• 21.1 versions prior to 21.1R2, 21.1R3;
• 21.2 versions prior to 21.2R1-S1, 21.2R2;

The examples of the config stanza affected by this issue:

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was discovered during external security research.

This issue has been assigned CVE-2021-31372 .

The following software releases have been updated to resolve this specific issue: 18.3R3-S5, 18.4R3-S9, 19.1R3-S6, 19.2R3-S3, 19.3R3-S3, 19.4R3-S5, 20.1R3-S1, 20.2R3-S2, 20.3R3-S1, 20.4R3, 21.1R2, 21.1R3, 21.2R1-S1, 21.2R2, 21.3R1, and all subsequent releases.

This issue is being tracked as 1594516 .

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

To reduce the risk of exploitation of this issue, use access lists or firewall filters to limit access to only trusted administrative networks, hosts and users.

Alternatively, J-Web can be disabled.

2021-10-13: 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 Vulnerability - How to Contact the Juniper Networks Security Incident Response Team
• CVE-2021-31372: J-Web allows a locally authenticated attacker to escalate their privileges to root

The Juniper SIRT would like to acknowledge and thank Andy Coles of Microsoft MSRC Vulnerabilities and Mitigations Team.