2019-07 Security Bulletin: Junos OS: Insufficient validation of environment variables in telnet client may lead to stack-based buffer overflow (CVE-2019-0053)

Product Affected:

This issue affects all products and platforms running Junos OS.

Problem:

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.

Solution:

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).

Workaround:

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

Implementation:

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

Modification History:

```
2019-07-10: Initial Publication
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CVSS Score:

7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)

Severity Level:

High

Severity Assessment:

Information for how Juniper Networks uses CVSS can be found at KB 16446 "Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."

Acknowledgements:

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.

Knowledge Base