CVE-2025-59957 is a vulnerability classified under CWE-346 (Origin Validation Error) found in Juniper Networks Junos OS running on EX4600 and QFX5000 Series switches. The root cause is insufficient protection of a critical configuration file (/etc/config/<platform>-defaults[-flex].conf) that can be modified by an unauthenticated attacker who has physical access to the device, but only if the device is not configured with a root password. By altering this file, the attacker can inject arbitrary configuration commands that are silently merged into the device's active configuration without operator visibility. This includes adding unauthorized users, IP addresses, or other configuration elements that grant persistent, stealthy control over the device. The backdoor persists across device reboots and even after zeroization (factory reset), making detection and remediation challenging. Detection involves comparing the suspect configuration file against a known clean version extracted from the original Junos OS image, a process supported by Juniper's Technical Assistance Center. Recovery requires a full system reinstall from physical media to ensure the device is restored to a trusted state. The vulnerability affects all Junos OS versions prior to 21.4R3 and 22.2 versions before 22.2R3-S3. The CVSS 3.1 base score is 6.8, reflecting a medium severity level due to the requirement of physical access and lack of remote exploitation, but with high impact on confidentiality, integrity, and availability if exploited. No public exploits have been reported to date.

For European organizations, this vulnerability poses a significant risk to network infrastructure security, particularly for those using Juniper EX4600 and QFX5000 Series switches. Exploitation allows attackers to establish persistent, stealthy backdoors that can compromise network integrity, confidentiality, and availability. This can lead to unauthorized access to sensitive data, interception or manipulation of network traffic, and potential disruption of critical services. The persistence of the backdoor even after device resets increases the difficulty of incident response and recovery, potentially prolonging exposure. Organizations in sectors with stringent regulatory requirements (e.g., finance, healthcare, critical infrastructure) face heightened compliance risks if such devices are compromised. The requirement for physical access limits the attack vector but does not eliminate risk, especially in environments with less controlled physical security or where devices are deployed in accessible locations. The stealthy nature of the attack complicates detection, increasing the risk of prolonged undetected compromise.

1. Immediately ensure that all Juniper EX4600 and QFX5000 Series devices are configured with strong root passwords to prevent unauthorized physical modification of configuration files. 2. Conduct integrity checks on the /etc/config/<platform>-defaults[-flex].conf file by comparing it against a clean version extracted from the original Junos OS image; coordinate with Juniper JTAC for extraction procedures. 3. Implement strict physical security controls to restrict unauthorized access to network devices, including locked cabinets and surveillance in data centers and network closets. 4. Regularly audit device configurations for unexpected or unauthorized changes, focusing on user accounts, IP addresses, and other critical settings. 5. Plan for and perform a full system reinstall from physical media if compromise is suspected to ensure complete removal of backdoors. 6. Monitor Juniper’s advisories for patches and apply updates to affected devices as soon as they become available. 7. Incorporate device configuration monitoring into security information and event management (SIEM) systems to detect anomalies promptly. 8. Train network operations staff to recognize signs of physical tampering and unusual device behavior.