A vulnerability in the telnetd Telnet server allows remote attackers to execute arbitrary code via short writes or urgent data, because of a buffer overflow involving the netclear and nextitem functions.

This issue only affects systems with inbound Telnet service enabled. SSH service is unaffected by this vulnerability.

This issue affects Juniper Networks Junos OS:

• 12.3 versions prior to 12.3R12-S16;
• 12.3X48 versions prior to 12.3X48-D105;
• 15.1 versions prior to 15.1R7-S7;
• 15.1X49 versions prior to 15.1X49-D220;
• 16.1 versions prior to 16.1R7-S8;
• 17.2 versions prior to 17.2R3-S4;
• 17.2X75 versions prior to 17.2X75-D45;
• 17.3 versions prior to 17.3R3-S8;
• 17.4 versions prior to 17.4R2-S11, 17.4R3-S2;
• 18.1 versions prior to 18.1R3-S10;
• 18.2 versions prior to 18.2R3-S5;
• 18.2X75 versions prior to 18.2X75-D34, 18.2X75-D41, 18.2X75-D430, 18.2X75-D65;
• 18.3 versions prior to 18.3R2-S4, 18.3R3-S3;
• 18.4 versions prior to 18.4R2-S5, 18.4R3-S4;
• 19.1 versions prior to 19.1R2-S2, 19.1R3-S2;
• 19.2 versions prior to 19.2R1-S5, 19.2R2;
• 19.3 versions prior to 19.3R2-S3, 19.3R3;
• 19.4 versions prior to 19.4R1-S3, 19.4R2-S1, 19.4R3;
• 20.1 versions prior to 20.1R1-S2, 20.1R2.

Telnet service is enabled via the following configuration stanza:

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

This issue has been assigned  CVE-2020-10188 .
 

The following software releases have been updated to resolve this specific issue: 12.3R12-S16, 12.3X48-D105, 15.1R7-S7, 15.1X49-D220, 15.1X49-D230, 16.1R7-S8, 17.2R3-S4, 17.2X75-D45, 17.3R3-S8, 17.3R3-S9, 17.4R2-S11, 17.4R3-S2, 18.1R3-S10, 18.2R3-S5, 18.2X75-D34, 18.2X75-D41, 18.2X75-D430, 18.2X75-D65, 18.3R2-S4, 18.3R3-S3, 18.4R2-S5, 18.4R3-S4, 19.1R2-S2, 19.1R3-S2, 19.2R1-S5, 19.2R2, 19.2R2-S1, 19.2R3, 19.3R2-S3, 19.3R3, 19.4R1-S3, 19.4R2-S1, 19.4R3, 20.1R1-S2, 20.1R2, 20.2R1, 20.3X75-D10, and all subsequent releases.

This issue is being tracked as  1502386 .
 

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

Avoid the use of Telnet service. Enable only SSH access for interactive login.

For example:

Use access lists or firewall filters to limit access to the device via Telnet only from trusted hosts.
 

2020-10-14: 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 Vulnerability - How to Contact the Juniper Networks Security Incident Response Team
• CVE-2020-10188 at cve.mitre.org