Cyber Resilience

CVE-2025-21590

Juniper Junos ≤ 21.2

CISA KEVActive ExploitationEUVD Exploited
Published
12 March 2025
Modified
24 October 2025
KEV Added
13 March 2025
Patch / advisory
View advisory
CVSS Score v4 6.7
Click a component to see what it means
Raw vectorCVSS: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
EPSS Score 0.017 75th percentile
Risk Priority 75 floored blend · peak EPSS

Summary

CVE-2025-21590 is a medium-severity Improper Isolation or Compartmentalization (CWE-653) vulnerability in Juniper Junos. Its CVSS base score is 6.7 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Escape to Host (T1611); ranked in the top 25% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.

The strongest mitigations our analysis identified map to SC-2 (Separation of System and User Functionality) and SC-3 (Security Function Isolation) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2025-21590 is an Improper Isolation or Compartmentalization vulnerability (CWE-653) in the kernel of Juniper Networks Junos OS. It enables a local attacker with high privileges to compromise the integrity of the device by injecting arbitrary code. The issue affects Junos OS versions prior to 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; and 24.2 versions before 24.2R1-S2 or 24.2R2. The vulnerability has a CVSS v3.1 base score of 4.4 (AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N) and was published on 2025-03-12.

A local attacker with shell access and high privileges can exploit this vulnerability to inject arbitrary code, leading to device integrity compromise. Exploitation is not possible from the Junos CLI, requiring prior shell access, which limits the attack surface to scenarios where an attacker has already achieved elevated local access.

The Juniper advisory (JSA93446) details mitigation through upgrading to the fixed releases listed for each affected version branch. CISA has added CVE-2025-21590 to its Known Exploited Vulnerabilities catalog, indicating real-world exploitation.

A Google Cloud threat intelligence blog highlights China-nexus espionage activity targeting Juniper routers, providing notable context for this vulnerability in active threat campaigns.

OWASP Top 10 for Web (2025)

A06:2025 Insecure Design

EU & UK References

Vulnerability Data

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…

more

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.

CWE(s)
CWE-653
KEV Date Added
13 March 2025

Related Threats

Threat-Actor AttributionAI

RedPenguin (C0056)
Ghost in the Router: China-Nexus Espionage Actor UNC3886 Targets Juniper Routers | Google Cloud Blog

MITRE ATT&CK Enterprise Techniques

T1611 Escape to Host Privilege Escalation
Adversaries may break out of a container or virtualized environment to gain access to the underlying host.
attack.mitre.org →
T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1134 Access Token Manipulation Stealth
Adversaries may modify access tokens to operate under a different user or system security context to perform actions and bypass access controls.
attack.mitre.org →
T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
attack.mitre.org →
T1548.001 Setuid and Setgid Privilege Escalation
An adversary may abuse configurations where an application has the setuid or setgid bits set in order to get code running in a different (and possibly more privileged) user’s context.
attack.mitre.org →
T1055 Process Injection Stealth
Adversaries may inject code into processes in order to evade process-based defenses as well as possibly elevate privileges.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2020-1631Same product: Juniper Junosboth on KEV
CVE-2023-28963Same product: Juniper Junos
CVE-2024-21601Same product: Juniper Junos
CVE-2024-30388Same product: Juniper Junos
CVE-2023-28962Same product: Juniper Junos
CVE-2024-47494Same product: Juniper Junos
CVE-2023-44188Same product: Juniper Junos
CVE-2023-22399Same product: Juniper Junos
CVE-2025-21591Same product: Juniper Junos
CVE-2026-21903Same product: Juniper Junos

Affected Assets

juniper
junos
21.2, 21.4, 22.2, 22.4, 23.2 · ≤ 21.2

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 8 hardening rules · 7 OS baselines
Validate
Prove the fix (OWASP ASVS)

—

Mitigating Controls (NIST 800-53 r5) AI

SC-3 Security Function Isolation good match

Security function isolation is the canonical mechanism for protecting higher-privilege compartments.

SC-39 Process Isolation good match

Process isolation maintains separate execution domains so one process cannot affect another’s privilege level.

SC-2 Separation of System and User Functionality good match

Explicit separation of user and management functionality implements the required compartmentalization.

SC-32 System Partitioning good match

System partitioning creates distinct domains that enforce isolation between differently privileged components.

AC-3 Access Enforcement partial match

Access enforcement directly requires approved authorizations to be applied to compartmentalized resources.

AC-4 Information Flow Enforcement partial match

Information flow enforcement structurally prevents unauthorized mixing of data or functions across privilege boundaries.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-05 full match
prevents

Least-privilege policy directly enforces separation of privilege levels and access rights.

PR.IR-01 mostly match
prevents

Network and environment segmentation implements the isolation required to prevent unauthorized cross-compartment access.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.3 Segregation of duties mostly match
degrades

Segregation of duties directly enforces separation of privilege levels and functions.

A.8.22 Segregation of networks mostly match
prevents

Network segregation is a classic technical control for isolating different privilege domains.

A.8.27 Secure system architecture and engineering principles mostly match
prevents

Secure system architecture principles explicitly call for isolation and least-privilege boundaries.

A.8.31 Separation of development, test and production environments mostly match
prevents

Separation of development, test and production environments is a direct application of compartmentalization.

A.5.15 Access control partial match
degrades

Access control policies establish the boundaries that isolation must enforce.

A.5.18 Access rights partial match
degrades

Managing access rights is the operational mechanism for compartmentalizing privileges.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Oracle Linux 9 (1 rule)
  • V-271452 OL 9 must use a Linux Security Module configured to enforce limits on system services. prevents CWE-653
RHEL 9 (2 rules)
  • V-258078 RHEL 9 must use a Linux Security Module configured to enforce limits on system services. prevents CWE-653
  • V-272496 RHEL 9 must elevate the SELinux context when an administrator calls the sudo command. prevents CWE-653
Windows 10 (1 rule)
  • V-220712 Only accounts responsible for the administration of a system must have Administrator rights on the system. prevents CWE-653
Windows 11 (1 rule)
  • V-253269 Only accounts responsible for the administration of a system must have Administrator rights on the system. prevents CWE-653
Windows Server 2016 (1 rule)
  • V-225007 Only administrators responsible for the member server or standalone or nondomain-joined system must have Administrator rights on the system. prevents CWE-653

References