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CISA KEV · ACTIVELY EXPLOITED
MEDIUM severity

CVE-2025-21590

MEDIUM

CVE-2025-21590 is a medium-severity (CVSS 4.4) CWE-653 vulnerability. It is in CISA's Known Exploited Vulnerabilities catalog (added 2025-03-13) — treat it as actively exploited and patch now. No vendor fix is recorded yet; mitigation options are listed below.

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…

Published
Updated
Affected
1 product
Patched
See advisory
Exploits
None indexed
Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, CISA KEV, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

  • Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2025-03-13. Federal agencies were required to remediate by 2025-04-03.
  • A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2025-21590.

EPSS Exploitation Probability

via FIRST.org ↗
1.7%probability of exploitation in next 30 days
Lower Risk+0.02%
Lower risk than most CVEs77th percentile — riskier than 77% of all scored CVEsHighest risk
0.27%0.93%1.59%2.25%0.8%1.7%1.7%1.7%Apr 26Oct 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2025-21590 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

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.

Affected Products

1 product · 79 configurations
OS
junosjuniper
< 21.2
7 versions
21.221.422.222.423.223.424.2

Detection & mitigation playbook

Vulnerability

  1. Detect

    Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).

  2. Remediation status

    No fixed release is recorded for CVE-2025-21590 yet. Track the upstream advisory, and apply the exposure-reduction steps below in the meantime.

  3. Mitigate without a patch

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

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 b
O3 Security · Impact-Aware SCA

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CVE-2025-21590: Medium 4.4 (KEV)