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

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• 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.

CISA’s summary

Juniper Junos OS contains an improper isolation or compartmentalization vulnerability. This vulnerability could allows a local attacker with high privileges to inject arbitrary code.

Weakness type: CWE-653.

Product: Juniper Junos OS · Assigned by: juniper · Published: 2025-03-12

Affected and fixed versions

Severity scores

• Attack vector: local access needed
• Attack complexity: low
• Attack requirements: none
• Privileges required: high (admin)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• 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.

Timeline

• 2025-03-12 — CVE record published by juniper
• 2025-03-13 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2025-04-03 — CISA remediation deadline for US federal agencies
• 2026-02-26 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. supportportal.juniper.net supportportal.juniper.net
2. Listed in CISA KEV notes (supportportal.juniper.net) supportportal.juniper.net

Vulnerability records

1. CVE.org record CVE-2025-21590 cve.org
2. NVD entry CVE-2025-21590 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov

Other references from the CVE record and advisory

1. cloud.google.com cloud.google.com

All exploited Juniper vulnerabilities · Today’s Security Digest