Junos OS: Insufficient validation of environment variables in telnet client may lead to stack-based buffer overflow

Description

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.

Scores

EPSS (exploitation in 30 days)

0.59% · top 52% of all CVEs (5 Nov 2026)

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.8.

Weakness

• CWE-121 Stack-based Buffer Overflow (opens in a new tab)All about CWE-121 and its CVEs
• CWE-787 (opens in a new tab)All about CWE-787 and its CVEs

Affected products

• Juniper Networks · Junos OS

  • affected 12.3 versions prior to 12.3R12-S13
  • affected 12.3X48 versions prior to 12.3X48-D80
  • affected 14.1X53 versions prior to 14.1X53-D130 and 14.1X53-D49
  • affected 15.1 versions prior to 15.1F6-S12 and15.1R7-S4
  • affected 15.1X49 versions prior to 15.1X49-D170
  • affected 15.1X53 versions prior to 15.1X53-D237 and 15.1X53-D496 and 15.1X53-D591 and 15.1X53-D69
  • affected 16.1 versions prior to 16.1R3-S11 and 16.1R7-S4
  • affected 16.2 versions prior to 16.2R2-S9
  • affected 17.1 versions prior to 17.1R3
  • affected 17.2 versions prior to 17.2R1-S8 and 17.2R2-S7 and 17.2R3-S1
  • affected 17.3 versions prior to 17.3R3-S4
  • affected 17.4 versions prior to 17.4R1-S6 and 17.4R2-S3 and 17.4R3
  • affected 18.1 versions prior to 18.1R2-S4 and 18.1R3-S3
  • affected 18.2 versions prior to 18.2R1-S5 and 18.2R2-S2 and 18.2R3
  • affected 18.2X75 versions prior to 18.2X75-D40
  • affected 18.3 versions prior to 18.3R1-S3 and 18.3R2
  • affected 18.4 versions prior to 18.4R1-S2 and 18.4R2

What to do

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.

Workaround: Since this issue is specific to outbound connections to a malicious host from the local telnet client, mitigation includes: * limit access to the Junos CLI and shell from only from trusted administrators * block outbound telnet connections * deny access to the telnet command and shell per user or user class

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

References (7)

• https://kb.juniper.net/JSA10947 (opens in a new tab)x_transferred
• https://www.exploit-db.com/exploits/45982 (opens in a new tab)x_transferred
• FreeBSD-SA-19:12 (opens in a new tab)vendor-advisoryx_transferred
• 20190724 FreeBSD Security Advisory FreeBSD-SA-19:12.telnet (opens in a new tab)mailing-listx_transferred
• http://packetstormsecurity.com/files/153746/FreeBSD-Security-Advisory-FreeBSD-SA-19-12.telnet.html (opens in a new tab)x_transferred
• [debian-lts-announce] 20221125 [SECURITY] [DLA 3205-1] inetutils security update (opens in a new tab)mailing-listx_transferred
• [debian-lts-announce] 20231008 [SECURITY] [DLA 3611-1] inetutils security update (opens in a new tab)mailing-listx_transferred

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2019-0053](https://trackcve.app/badge/CVE-2019-0053.svg)](https://trackcve.app/cve/CVE-2019-0053)

Record last updated 16 Sept 2024, 19:15 UTC.