Unauth Backdoor via /etc/config on Junos OS <21.4R3/22.2R3-S3
CVE-2025-59957 Published on October 9, 2025
Junos OS: EX4600 Series and QFX5000 Series: An attacker with physical access can open a persistent backdoor
An Origin Validation Error vulnerability in an insufficient protected file of Juniper Networks Junos OS on EX4600 Series and QFX5000 Series allows an unauthenticated attacker with physical access to the device to create a backdoor which allows complete control of the system.
When a device isn't configured with a root password, an attacker can modify a specific file. It's contents will be added to the Junos configuration of the device without being visible. This allows for the addition of any configuration unknown
to the actual operator, which includes users, IP addresses and other configuration which could allow unauthorized access to the device.
This exploit is persistent across reboots and even zeroization.
The indicator of compromise is a modified /etc/config/<platform>-defaults[-flex].conf file. Review that file for unexpected configuration statements, or compare it to an unmodified version which can be extracted from the original Juniper software image file. For details on the extraction procedure please contact Juniper Technical Assistance Center (JTAC).
To restore the device to a trusted initial configuration the system needs to be reinstalled from physical media.
This issue affects Junos OS on EX4600 Series and QFX5000 Series:
* All versions before 21.4R3,
* 22.2 versions before 22.2R3-S3.
Vulnerability Analysis
CVE-2025-59957 can be exploited with physical access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Type
Origin Validation Error
The software does not properly verify that the source of data or communication is valid.
Products Associated with CVE-2025-59957
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Affected Versions
Juniper Networks Junos OS:- Before 21.4R3 is affected.
- Version 22.2 and below 22.2R3-S3 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.