Impact
The impact of CVE-2025-21590 can be severe, as the flaw enables local attackers with high-level privileges to compromise the affected system.
This includes:
Privilege escalation: Attackers can escalate their privileges within the system, leading to unauthorized control.
Potential full system compromise: With arbitrary code execution, attackers can gain control over critical systems, access sensitive data, or disrupt operations.
Organizations using outdated Juniper devices or vulnerable versions of Junos OS face significant risks, including the potential for data theft, disruption of services, and long-term security breaches.
March 17 2025 - Juniper
Juniper Junos OS Improper Isolation Vulnerability Exploited in Wild (CVE-2025-21590)
Severity Level: 2
Recently, our Threat Intel Team has come across a significant security vulnerability in Juniper Networks
Junos OS, identified as CVE-2025-21590. This vulnerability arises from an improper isolation issue within
the operating system's kernel, which could allow a local attacker with elevated privileges to execute arbitrary
code. The flaw could lead to privilege escalation, system compromise, and potential data breaches if
successfully exploited. The vulnerability is specifically tied to older versions of Junos OS, and while
exploitation requires high-level access to the system, it still poses significant risks to the confidentiality and
integrity of affected networks and devices.
Technical Details
The vulnerability stems from inadequate security restrictions in Junos OS, which could be exploited by a local attacker with shell access. An attacker could exploit this flaw to execute unauthorized code, leading to privilege escalation, system compromise, and potentially full control over affected devices.
Key technical points include:
The vulnerability is confined to devices with local access to the operating system, meaning exploitation is not possible via the Junos command-line interface (CLI).
Affected devices are primarily those running older versions of Junos OS.
The exploitation of this vulnerability requires high-level privileges, which means only trusted users with elevated system access can take advantage of the flaw.
Detection Method
To detect if your systems are vulnerable to CVE-2025-21590, the following actions are recommended:
Review system logs and access controls: Look for any unauthorized shell access or abnormal behaviour within the system logs.
Monitor system processes: Any signs of unusual code execution or process manipulation should be treated as potential indicators of exploitation.
Check Junos OS version: Ensure that devices are running the latest versions of Junos OS. Vulnerable systems are typically those running older, unsupported versions of the software.
Use automated security tools: Employ security tools that can help identify vulnerabilities and abnormal system activities related to the exploitation of this flaw.
Also, this issue affects Junos OS 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.
Indicators of Compromise
No Indicators of Compromise
Recommendations
Organizations should take immediate action to mitigate the risk associated with CVE-2025-21590. Recommended steps include:
Upgrade Junos OS: Apply the security patches and upgrades released by Juniper Networks as outlined in advisories JSA93446 and JSA5385.
The software releases updated to resolve this specific issue are: 21.2R3-S9*, 21.4R3-S10, 22.2R3-S6, 22.4R3-S6, 23.2R2-S3, 23.4R2-S4*, 24.2R1-S2, 24.2R2, 24.4R1, and all subsequent releases.
These updates address CVE-2025-21590 and include critical anti-malware signature updates.
Limit shell access: Restrict shell access to trusted users only. Implement strict access control policies to prevent unauthorized access.
Implement multi-factor authentication (MFA): Strengthen authentication processes to make it harder for attackers to gain unauthorized access.
Enforce role-based access control (RBAC): Ensure that only authorized personnel have high-level privileges to minimize the risk of privilege escalation.
Discontinue support for end-of-life devices: If using end-of-life Juniper routers that no longer receive support or security updates, consider discontinuing use or replacing them with supported models.
Monitor and respond to threats: Continuously monitor systems for any signs of exploitation, particularly on devices running unsupported software versions.
Conclusion
CVE-2025-21590 represents a critical vulnerability in Junos OS that poses a significant risk to the integrity and security of affected devices. Exploitation of this vulnerability could lead to privilege escalation and full system compromise. While the flaw requires high-level privileges for exploitation, it remains a serious concern, particularly for systems running outdated versions of Junos OS. CISA, Mandiant, and Juniper Networks strongly advise all organizations, particularly those in federal sectors, to take immediate steps to remediate the vulnerability. Upgrading to the latest Junos OS versions, restricting shell access, and enforcing robust access controls are crucial measures to reduce the risk of exploitation.