How severe is CVE-2025-21590?

CVE-2025-21590 has a CVSS score of 4.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which products are affected by CVE-2025-21590?

Affected package information for CVE-2025-21590 is not yet fully mapped. Check the official advisory links for details.

How do I patch CVE-2025-21590?

No patch has shipped for CVE-2025-21590 yet — track the juniper junos advisory for a fixed release and apply the workarounds below in the meantime.

How do I detect CVE-2025-21590 across my infrastructure?

Inventory every juniper junos deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for remote code execution at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.

How do I mitigate CVE-2025-21590 if there is no patch (or I can't update yet)?

Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.

How does O3 Security protect against CVE-2025-21590?

O3 detects and blocks CVE-2025-21590 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.

Is CVE-2025-21590 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-21590 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2025-21590?

CVE-2025-21590 has an EPSS (Exploit Prediction Scoring System) score of 1.7%, placing it in the 74th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

Is CVE-2025-21590 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2025-21590 (Juniper Junos OS Improper Isolation or Compartmentalization Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2025-03-13. CISA required all US federal civilian agencies to remediate this vulnerability by 2025-04-03. The required action was: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2025-21590?

CVE-2025-21590 is classified as CWE-653 (CWE-653). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Which products and versions are affected by CVE-2025-21590?

CVE-2025-21590 affects juniper junos (7 versions, e.g. 21.2, 21.4, 22.2…). Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2025-21590 published, and has it been updated?

CVE-2025-21590 was published on March 12, 2025 and was last updated on June 17, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2025-03-13 — agencies required to remediate by 2025-04-03

CVE-2025-21590

MEDIUM

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…

Published

Mar 12, 2025

Updated

Jun 17, 2026

Affected

0 pkgs

Patched

None yet

Exploits

None indexed

EPSS Exploitation Probability

via FIRST.org ↗

1.7%probability of exploitation in next 30 days

Lower Risk74th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

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.

Affected Products

1 product · 82 configurations

junosjuniper

≤ 21.2

7 versions

21.221.422.222.423.223.424.2

Detection & mitigation playbook

Vendor / appliance

Detect
Inventory every juniper junos deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for remote code execution at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
Remediation status
No patch has shipped for CVE-2025-21590 yet — track the juniper junos advisory for a fixed release and apply the workarounds below in the meantime.
Mitigate without a patch
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2025-21590 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.

Tailored to CVE-2025-21590. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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 b

O3 Security · Runtime Protection

Is CVE-2025-21590 being exploited in your environment?

O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2025-21590 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.

Protect my workloads How runtime protection works

CVE-2025-21590

EPSS Exploitation Probability

Description

Affected Products

Detection & mitigation playbook

Detect

Remediation status

Mitigate without a patch

How O3 protects you

Frequently Asked Questions

Is CVE-2025-21590 being exploited in your environment?