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2020-10 Security Bulletin: Junos OS: Arbitrary code execution vulnerability in Telnet server (CVE-2020-10188)

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Article ID: JSA11057 SECURITY_ADVISORIES Last Updated: 14 Oct 2020Version: 1.0
Product Affected:
This issue affects Junos OS 12.3, 12.3X48, 15.1, 15.1X49, 16.1, 17.2, 17.2X75, 17.3, 17.4, 18.1, 18.2, 18.2X75, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1.
Problem:

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:

[system services telnet]
 

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

This issue has been assigned CVE-2020-10188.
 

Solution:

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.
 

Workaround:

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

For example:

# delete system services telnet
# set system services ssh
# commit

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

Implementation:
Software releases or updates are available for download at https://www.juniper.net/support/downloads/.
Modification History:
2020-10-14: Initial Publication

CVSS Score:
9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
Severity Level:
Critical
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."

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