Known exploited vulnerability · CISA KEV

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

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

CVE-2025-21590

Exploited in the wild. Fix this first.

CISA added it to the Known Exploited Vulnerabilities catalog on 2025-03-13: attackers are using it right now.

CISA KEV: Listed; Added 2025-03-13 · federal fix-by 2025-04-03
EPSS (30 days): 1.7%; Higher than 78% of CVEs · 2026-11-01
CVSS v4.0: 6.7 Medium; 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

What CISA says

Juniper Junos OS Improper Isolation or Compartmentalization Vulnerability

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

NVD description · published 2025-03-12

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.

Full record on NVD

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How to check if you are exposed to CVE-2025-21590

Find every Juniper Junos OS system you or your clients run, including ones exposed to the internet. Those come first: CISA only lists flaws attackers are already using.
Compare each version with the fixed versions in the vendor advisory below. Where no fix exists yet, apply the vendor’s mitigation or take the system off the internet.
Run a credentialed vulnerability scan to catch the systems you missed, then check that the next scan no longer reports CVE-2025-21590.

US federal agencies had to fix this by 2025-04-03. Everyone else should treat that deadline as a guide: if it has passed, this is overdue.

Affected versions

Versions the National Vulnerability Database lists as vulnerable to CVE-2025-21590. Check the vendor advisory for the exact fixed builds before you sign anything off.

Product	Vulnerable versions
Juniper Junos	before 21.2; 21.2; 21.2-r1; 21.2-r1-s1; 21.2-r1-s2; 21.2-r2 and 73 more

Timeline

2025-03-12 · Published in the National Vulnerability Database
2025-03-13 · Added to CISA's Known Exploited Vulnerabilities catalog, 1 day after it was published
2025-04-03 · Fix-by date for US federal agencies, passed 577 days ago

Vendor advisories and fixes

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

Weakness type

CWE-653

More exploited Juniper vulnerabilities

CISA lists 8 exploited Juniper vulnerabilities. The closest matches:

Keep going

Sources: CISA Known Exploited Vulnerabilities catalog (version 2026.10.30); EPSS data from FIRST.org; CVSS and descriptions from the NIST National Vulnerability Database. Checked 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.