Exploited

CVE-2025-21590

Juniper Junos OS · Switches, routers and SD-WAN

Juniper Junos OS Improper Isolation or Compartmentalization Vulnerability

At a glance

Exploited. Added to CISA’s catalog of exploited vulnerabilities on March 13, 2025.

Affected product: Juniper Junos OS (category Switches, routers and SD-WAN, indicative classification). Name in CISA’s catalog: Juniper Junos OS.

What should I do?

Apply the patches or mitigations from Juniper; if none are available, stop using the product. For cloud services, follow the guidance from Juniper.

Deadline set by CISA for US federal agencies: 21 days (due April 3, 2025). It only binds those agencies, but it is a useful measure of urgency.

Juniper security advisories page (general page, not the advisory for this vulnerability)
The vendor’s specific advisory is listed in the NVD references: CVE-2025-21590 on the NVD website.

Original text of the 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.

Timeline

March 12, 2025 Vulnerability published Publication date (NVD)
March 13, 2025 Exploitation confirmed Added to CISA’s KEV catalog
April 3, 2025 CISA deadline Remediation deadline set for US federal agencies

The facts, with their sources

Exploitation confirmed: Yes, on March 13, 2025 Date added to the catalog of exploited vulnerabilities. Exploitation itself may have started earlier. Source: KEV catalog, collected September 29, 2026 at 11:25 UTC
Ransomware: No known use to date That does not guarantee it is not being used: the information is not public. Source: KEV catalog, collected September 29, 2026 at 11:25 UTC
Hunt for compromise: Not requested by CISA Source: KEV catalog, collected September 29, 2026 at 11:25 UTC
CISA required action: Apply the patches or mitigations from Juniper; if none are available, stop using the product. For cloud services, follow the guidance from Juniper. Rewritten by this site from CISA’s original text. Source: KEV catalog, collected September 29, 2026 at 11:25 UTC
CISA deadline: April 3, 2025, 21 days Set for US federal agencies: a measure of urgency, not an obligation elsewhere. Source: KEV catalog, collected September 29, 2026 at 11:25 UTC
Vulnerability published: March 12, 2025 Source: National Vulnerability Database (NVD), collected September 29, 2026 at 11:29 UTC
Product according to CISA: Juniper Junos OS Filed by this site under “Switches, routers and SD-WAN” (indicative classification). Source: KEV catalog, collected September 29, 2026 at 11:25 UTC
CVSS vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N Technical detail of the score: attack vector, complexity, impact. Source: National Vulnerability Database (NVD), collected September 29, 2026 at 11:29 UTC

Severity and activity

4.4 / 10 CVSS severity: medium

Score from the vendor or CISA, relayed by the NVD. Collected Sep 29, 2026.

— Probability of exploitation in the next 30 days (EPSS)

FIRST’s EPSS model. Since exploitation is already confirmed, this figure is mostly useful to compare activity. Collected Sep 29, 2026.

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.

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

Summary from CISA (KEV catalog).

CERT-FR advisories

No advisory among the latest CERT-FR publications this site follows. That does not mean there are none.

Information reused under the Open Licence 2.0 (Etalab); the date of last update is shown for each advisory. This site is neither affiliated with nor endorsed by ANSSI.

Sources for this page

CISA KEV catalog: exploitation, date added, required action, deadline, ransomware.
NVD (NIST): CVSS severity, publication date, description, vendor references.
EPSS (FIRST): probability of exploitation.
CERT-FR: advisories and alerts (in French).
Brand and category: indicative classification by this site (method).