CVE Intelligence
CISA KEV Medium

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

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.

Published Mar 12, 2025 · Updated Oct 13, 2026 · Sources: CISA Known Exploited Vulnerabilities, NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: juniper

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

CISA KEV · Mar 13, 2025 ☠ UNC3886
How the score was calculated
  • Confirmed exploitation (CISA KEV)+35
  • Exploited by 1 threat actor(s) (MITRE ATT&CK)+10
  • EPSS 1.7% (30-day exploitation probability)+12
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Confirmed
CISA KEV, listed Mar 13, 2025
EPSS FIRST
1.74%
ahead of 77% of scored CVEs · Oct 14, 2026
Affects
Juniper Networks
Junos and 1 more
CVSS base
4.4
Medium · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
Active
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Total
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

CISA required action CISA

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

US federal deadline: Apr 3, 2025 — passed 560 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Juniper Networks Junos, Juniper Networks Junos OS).
  2. Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
  3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  4. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Juniper Networks Junos version 22.4-r1-s1version 22.4-r3-s4version 22.4-r3-s3version 22.4-r3-s2version 22.4-r3-s1version 22.4-r3version 22.4-r2-s2version 22.4-r2-s1
and 71 more version 22.4-r2version 22.4-r1-s2version 22.4-r3-s5version 22.4-r1version 22.4version 22.2-r3-s5version 22.2-r3-s4version 22.2-r3-s3version 22.2-r3-s2version 22.2-r3-s1version 22.2-r3version 22.2-r2-s2version 23.4-r1-s1version 24.2-r2version 24.2-r1-s1version 24.2-r1version 24.2version 23.4-r2-s3version 23.4-r2-s2version 23.4-r2-s1version 23.4-r2version 23.4-r1-s2version 21.2version 23.4-r1version 23.4version 23.2-r2-s2version 23.2-r2-s1version 23.2-r2version 23.2-r1-s2version 23.2-r1-s1version 23.2-r1version 23.2version 21.2-r3-s2version 21.4-r1-s1version 21.4-r1version 21.4version 21.2-r3-s8version 21.2-r3-s7version 21.2-r3-s6version 21.2-r3-s5version 21.2-r3-s4version 21.2-r3-s3version 22.2-r2version 21.2-r3-s1version 21.2-r3version 21.2-r2-s2version 21.2-r2-s1version 21.2-r2version 21.2-r1-s2version 21.2-r1-s1version 21.2-r1< 21.2version 21.4-r2version 22.2-r2-s1version 22.2-r1-s2version 22.2-r1-s1version 22.2-r1version 22.2version 21.4-r3-s9version 21.4-r3-s8version 21.4-r3-s7version 21.4-r3-s6version 21.4-r3-s5version 21.4-r3-s4version 21.4-r3-s3version 21.4-r3-s2version 21.4-r3-s1version 21.4-r3version 21.4-r2-s2version 21.4-r2-s1version 21.4-r1-s2
Vulnerable NIST National Vulnerability Database
Juniper Networks Junos OS < 21.2R3-S9≥ 21.4 and < 21.4R3-S10≥ 22.2 and < 22.2R3-S6≥ 22.4 and < 22.4R3-S6≥ 23.2 and < 23.2R2-S3≥ 23.4 and < 23.4R2-S4≥ 24.2 and < 24.2R1-S2, 24.2R2 Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Local
Attack complexity
Low
Privileges required
High
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
6.7 CVSS 4.0 Medium — — sirt@juniper.net via NIST National Vulnerability Database
6.7 CVSS 4.0 Medium — — juniper via CVE Program (cve.org) e CISA ADP
4.4 CVSS 3.1 Medium 0.8 3.6 sirt@juniper.net via NIST National Vulnerability Database
4.4 CVSS 3.1 Medium — — GitHub, Inc. via GitHub Security Advisories
4.4 CVSS 3.1 Medium — — juniper via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N (score shown at the top: sirt@juniper.net)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-653

Other CVEs with this weakness →

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

Listed
Mar 13, 2025
Federal deadline
Apr 3, 2025
passed 560 day(s) ago
Ransomware use
Unknown

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

Threat actors exploiting this CVE MITRE ATT&CK

According to MITRE ATT&CK.

UNC3886 G1048

EPSS over time FIRST

Oct 12, 2026 → Oct 14, 2026 · 3 reading(s) · max 1.74%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
  • Hunt retroactively in logs from before Mar 13, 2025 (KEV listing): exploitation may have started earlier.
endpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · juniper networks/junos os
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Affected products added · juniper/junos
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 4.4
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Added to CISA KEV (detected)
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • Record created in this database
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • 2025
  • Added to CISA KEV catalog
    Mar 12, 2025 · CISA
  • CVE published
    Mar 12, 2025 · juniper

Source activity

Repeated readings are counted rather than listed.

  • 2× References added · Oct 13, 2026 – Oct 13, 2026
  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

5 on the record

Elsewhere on this site

Juniper Networks
every CVE for this vendor
2025-03
what else CISA listed that month
CWE-653
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-102077 Junos OS: MX Series with SPC3: In a source NAT scenario malformed packets will lead to resource leaks and eventually traffic stops 1d
  • CVE-2026-101982 Junos OS and Junos OS Evolved: A EVPN peer causes an rpd crash or root-level compromise when EVPN-VPWS is used 1d
  • CVE-2026-101983 Junos OS and Junos OS Evolved: An attacker causes remote code execution when J-Web virtual-domain is configured 1d
  • CVE-2026-101964 Junos OS and Junos OS Evolved: An attacker can cause an rpd crash via a crafted LDP message 1d
  • CVE-2026-101975 Junos OS and Junos OS Evolved: Improper OSPF LSA validation causes an rpd crash when prefix-SID best-route installation is used 1d
  • CVE-2026-101972 Junos OS and Junos OS Evolved: Malformed OSPF packets causes routing disruption when OSPF is enabled 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2025-21590 is "Juniper Junos OS Improper Isolation or Compartmentalization Vulnerability", rated Medium. It affects Junos (Juniper Networks); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 4.4 describes technical severity. EPSS 1.74% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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