Insufficient validation of environment variables in the telnet client supplied in Junos OS can lead to stack-based buffer overflows, which can be exploited to bypass veriexec restrictions on Junos OS. A stack-based overflow is present in the handling of environment variables when connecting via the telnet client to remote telnet servers.

This issue only affects the telnet client — accessible from the CLI or shell — in Junos OS. Inbound telnet services are not affected by this issue.

This issue affects Juniper Networks Junos OS:

• 12.3 versions prior to 12.3R12-S13;
• 12.3X48 versions prior to 12.3X48-D80;
• 14.1X53 versions prior to 14.1X53-D130, 14.1X53-D49;
• 15.1 versions prior to 15.1F6-S12, 15.1R7-S4;
• 15.1X49 versions prior to 15.1X49-D170;
• 15.1X53 versions prior to 15.1X53-D237, 15.1X53-D496, 15.1X53-D591, 15.1X53-D69;
• 16.1 versions prior to 16.1R3-S11, 16.1R7-S4;
• 16.2 versions prior to 16.2R2-S9;
• 17.1 versions prior to 17.1R3;
• 17.2 versions prior to 17.2R1-S8, 17.2R2-S7, 17.2R3-S1;
• 17.3 versions prior to 17.3R3-S4;
• 17.4 versions prior to 17.4R1-S6, 17.4R2-S3, 17.4R3;
• 18.1 versions prior to 18.1R2-S4, 18.1R3-S3;
• 18.2 versions prior to 18.2R1-S5, 18.2R2-S2, 18.2R3;
• 18.2X75 versions prior to 18.2X75-D40;
• 18.3 versions prior to 18.3R1-S3, 18.3R2;
• 18.4 versions prior to 18.4R1-S2, 18.4R2.

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-2019-0053 .
 

The following software releases have been updated to resolve this specific issue: 12.3R12-S13, 12.3X48-D80, 12.3X48-D85, 14.1X53-D130, 14.1X53-D49, 15.1F6-S12, 15.1R7-S4, 15.1X49-D170, 15.1X53-D237, 15.1X53-D496, 15.1X53-D591, 15.1X53-D69, 16.1R3-S11, 16.1R7-S4, 16.2R2-S9, 17.1R3, 17.2R1-S8, 17.2R2-S7, 17.2R3-S1, 17.3R3-S4, 17.4R1-S6, 17.4R2-S3, 17.4R3, 18.1R2-S4, 18.1R3-S3, 18.2R1-S5, 18.2R2-S2, 18.2R3, 18.2X75-D40, 18.3R1-S3, 18.3R2, 18.4R1-S2, 18.4R2, 19.1R1, and all subsequent releases.

This issue is being tracked as PR  1409847  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).
 

Software Releases, patches and updates are available at  https://www.juniper.net/support/downloads/ .
 

Since this issue is specific to outbound telnet connections to a malicious host from the local telnet client, mitigation includes:

• limiting access to the Junos CLI and shell from only from trusted administrators
• blocking outbound telnet connections via a stateless firewall filter
• denying access to the ' telnet ' command and the Junos shell

• ​2019-07-10: 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-2019-0053 at cve.mitre.org

The Juniper SIRT would like to would like to acknowledge and thank Matthew Hickey, Hacker House ( https://hacker.house/ ), who reported this issue on November 12, 2018.