Threat Intelligence / CVE / CVE-2025-21590

CVE-2025-21590 — Juniper Junos

CISA KEV

CVSS v3.1 4.4 (MEDIUM) · CVSS v4.0 6.7 · EPSS 0.7% (higher than 73.6% of all scored CVEs) · Priority 9/10 · Published 2025-03-12

As of 2025-10-24, CVE-2025-21590 is a MEDIUM-severity vulnerability in Juniper Junos, CVSS v3.1 4.4, EPSS 0.7% (73.6th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2025-03-13), with a US federal remediation deadline of 2025-04-03. Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2025-21590, most recently “UNC3886 Zero-Day Rootkit Campaign Targeting Singaporean Telecommunications — ORB Network C2, Fortinet/VMware Exploitation, Covert Infrastructure Persistence”.

Last updated: 2025-10-24

What is CVE-2025-21590?

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.

The record classifies CVE-2025-21590 under weakness class CWE-653. Its CVSS v3 base vector states that the flaw requires local access to the host, needs high-privilege credentials, needs no user interaction, and has high impact on integrity. 82 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 550 days ago.

Severity and exploitation probability

CVSS v3.1 base score: 4.4 — MEDIUM
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
CVSS v4.0 base score: 6.7
EPSS (FIRST): 0.7% probability of exploitation in the next 30 days, higher than 73.6% of all scored CVEs
CISA KEV: Listed since 2025-03-13, federal remediation deadline 2025-04-03
Threadlinqs priority: 9/10 — CISA KEV-listed, which Threadlinqs floors at 9
Published: 2025-03-12, last modified 2025-10-24

Is CVE-2025-21590 being exploited?

CISA added CVE-2025-21590 to the Known Exploited Vulnerabilities catalog on 2025-03-13, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2025-04-03 under BOD 22-01. It currently carries a trending score of 33 in the Threadlinqs vulnerability feed.

Affected products and versions

Juniper: Junos, Junos 21.2, Junos 21.4, Junos 22.2, Junos 22.4, Junos 23.2, Junos 23.4, Junos 24.2

Showing 8 of 82 recorded product entries.

How to fix CVE-2025-21590

The record marks a vendor fix as available for CVE-2025-21590. Vendor advisory: https://supportportal.juniper.net/JSA93446. Because CVE-2025-21590 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2025-04-03. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

Threat activity tracking CVE-2025-21590

1 tracked threat in the Threadlinqs corpus references CVE-2025-21590, either in the campaign’s CVE list or as an indicator on the campaign record.

UNC3886 Zero-Day Rootkit Campaign Targeting Singaporean Telecommunications — ORB Network C2, Fortinet/VMware Exploitation, Covert Infrastructure Persistence — CRITICAL · 2026-03-13

Sources

Seeded from NVD and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.

Full detection coverage & IOCs for threats exploiting CVE-2025-21590 are available via the Threadlinqs MCP server (Purple tier). View plans →

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