The improper handling of client-side parameters in J-Web of Juniper Networks Junos OS allows an attacker to perform a number of different malicious actions against a target device when a user is authenticated to J-Web. An attacker may be able to supersede existing parameters, including hardcoded parameters within the HTTP/S session, access and exploit variables, bypass web application firewall rules or input validation mechanisms, and otherwise alter and modify J-Web's normal behavior. An attacker may be able to transition victims to malicious web services, or exfiltrate sensitive information from otherwise secure web forms.

This issue affects:

Juniper Networks Junos OS:

• All versions prior to 17.4R3-S3;
• 18.1 versions prior to 18.1R3-S12;
• 18.2 versions prior to 18.2R3-S6;
• 18.3 versions prior to 18.3R3-S4;
• 18.4 versions prior to 18.4R3-S6;
• 19.1 versions prior to 19.1R3-S4;
• 19.2 versions prior to 19.2R3-S1;
• 19.3 versions prior to 19.3R3-S1;
• 19.4 versions prior to 19.4R2-S2, 19.4R3;
• 20.1 versions prior to 20.1R2;
• 20.2 versions prior to 20.2R2.

This issue requires J-Web to be enabled on the device.

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 found during internal product security testing or research.

This issue has been assigned  CVE-2021-0269 .

The following software releases have been updated to resolve this specific issue: 17.4R3-S3, 18.1R3-S12, 18.2R3-S6, 18.3R3-S4, 18.4R3-S6, 19.1R3-S4, 19.2R3-S1, 19.3R3-S1, 19.4R2-S2, 19.4R3, 20.1R2, 20.2R2, 20.3R1, and all subsequent releases.

This issue is being tracked as  1501588 .

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

To reduce the risk of exploitation utilize common security BCPs to limit the exploitable surface by limiting access to network and device to trusted systems, administrators, networks and hosts.

Access the J-Web service from trusted hosts which may not be compromised by cross-site scripting attacks, for example, deploying jump hosts with no internet access.

Alternatively, disable J-Web.

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-2021-0269 at cve.mitre.org