---
title: "CVE-2025-21590: Juniper Junos OS Improper Isolation or Compartmentalization Vulnerability"
url: https://erroneo.us/security/cve/CVE-2025-21590/
description: "CVE-2025-21590 (Juniper Junos OS): Exploited in the wild (CISA KEV). An Improper Isolation or Compartmentalization vulnerability in the kernel of Juniper…"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-03-12
date_modified: 2026-02-26
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2025-21590"
kev: true
cvss: 6.7
epss: 0.01735
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2025-21590: Juniper Junos OS Improper Isolation or Compartmentalization Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Juniper Junos OS. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-03-13, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-04-03 ; treat that as the outer limit, not the target.
- EPSS 1.7% , percentile 77: FIRST’s model estimates a 1.7% chance of exploitation activity in the next 30 days, higher than 77% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.

## What it is

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.

## Affected products (CVE record)

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

## Severity

- juniper CVSS 3.1: 4.4 `CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N`
- juniper CVSS 4.0: 6.7 `CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`

## Exploitation

- CISA KEV: added 2025-03-13; federal due date 2025-04-03. Known ransomware use: Unknown.
- CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- CISA SSVC assessment: exploitation active , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 1.74% probability of exploitation activity in the next 30 days; percentile 77.

## Sources

- [supportportal.juniper.net](https://supportportal.juniper.net/JSA93446)
- [Listed in CISA KEV notes (supportportal.juniper.net)](https://supportportal.juniper.net/s/article/2025-03-Out-of-Cycle-Security-Bulletin-Junos-OS-A-local-attacker-with-shell-access-can-execute-arbitrary-code-CVE-2025-21590?language=en_US)
- [CVE.org record CVE-2025-21590](https://www.cve.org/CVERecord?id=CVE-2025-21590)
- [NVD entry CVE-2025-21590](https://nvd.nist.gov/vuln/detail/CVE-2025-21590)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21590)
- [cloud.google.com](https://cloud.google.com/blog/topics/threat-intelligence/china-nexus-espionage-targets-juniper-routers)

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Source page: https://erroneo.us/security/cve/CVE-2025-21590/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt