Juniper Junos OS Improper Isolation or Compartmentalization
CVE-2025-21590 is a medium-severity improper isolation or compartmentalization vulnerability in Junos OS from Juniper Networks, with a CVSS 3.1 base score of 4.4 out of 10. It can be exploited with local access to the system by an attacker with administrator privileges, without any action from a user. The record lists versions 21.2R3-S9, 21.4R3-S10, 22.2R3-S6 as the first without the flaw, so updating Junos OS to one of those releases or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on March 13, 2025, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Junos OS to 21.2R3-S9 or 21.4R3-S10 or 22.2R3-S6 or 22.4R3-S6, whichever matches your release line, or a later version.
- Update Junos to 21.2 or a later version.
- CISA's 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.
- Read the advisory on supportportal.juniper.net for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Juniper Networks | Junos OS | before 21.2R3-S9; 21.4 up to, but not including, 21.4R3-S10; 22.2 up to, but not including, 22.2R3-S6; 22.4 up to, but not including, 22.4R3-S6; 23.2 up to, but not including, 23.2R2-S3; 23.4 up to, but not including, 23.4R2-S4; 24.2 up to, but not including, 24.2R1-S2, 24.2R2 | 21.2R3-S9, 21.4R3-S10, 22.2R3-S6, 22.4R3-S6, 23.2R2-S3, 23.4R2-S4 |
| Juniper Networks | Junos | before 21.2; 21.2; 21.4; 22.2; 22.4; 23.2; 23.4; 24.2 | 21.2 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- HighAdministrator-level access is required first.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N. Scored by CNA (juniper.net).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 6.7 | Medium | CNA (juniper.net) |
| CVSS 3.1 | 4.4 | Medium | CNA (juniper.net) |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Isolation or Compartmentalization
The product does not properly compartmentalize or isolate functionality, processes, or resources that require different privilege levels, rights, or permissions.
How developers prevent this class of flaw
- Break up privileges between different modules, objects, or entities. Minimize the interfaces between modules and require strong access control between them.
More Improper Isolation or Compartmentalization vulnerabilities (CWE-653)
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
- Deadline for US federal agencies to remediate, set by CISA.
- Record last changed materially (score, affected products, status or references).
References
Advisories
Third-party and government advisories
- cloud.google.com/blog/topics/threat-intelligence/china-nexus-espionage-targets-juniper-routersThird Party Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21590US Government Resource
Other vulnerabilities in Junos OS
- 7.5 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 8.8 High severity
- 8.8 High severity
- 7.5 High severity
Recent Improper Isolation or Compartmentalization vulnerabilities
- 8.4 High severity
- 7.6 High severity
- 8.8 High severity
- 8.2 High severity
- 8.1 High severity
Spotted an error? Tell us.