Juniper Junos OS up to 21.4R2/22.2R3-S2 -defaults[-flex].conf origin validation

Summaryinfo

A vulnerability classified as critical has been found in Juniper Junos OS up to 21.4R2/22.2R3-S2. Impacted is an unknown function of the file /etc/config/-defaults[-flex].conf. This manipulation causes origin validation. The identification of this vulnerability is CVE-2025-59957. It is feasible to perform the attack on the physical device. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in Juniper Junos OS up to 21.4R2/22.2R3-S2 and classified as critical. Affected by this vulnerability is some unknown processing of the file /etc/config/-defaults[-flex].conf. The manipulation with an unknown input leads to a origin validation vulnerability. The CWE definition for the vulnerability is CWE-346. The product does not properly verify that the source of data or communication is valid. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at supportportal.juniper.net. This vulnerability is known as CVE-2025-59957 since 09/23/2025. The exploitation appears to be easy. Attacking locally is a requirement. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 01/24/2026).

The vulnerability scanner Nessus provides a plugin with the ID 269724 (Juniper Junos OS Vulnerability (JSA103146)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 21.4R3 or 22.2R3-S3 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (269724) and CERT Bund (WID-SEC-2025-2238). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

• Juniper JUNOS

Productinfo

Type

• Router Operating System

Vendor

• Juniper

Name

• Junos OS

Version

• 21.4R2
• 22.2R3-S2

License

• commercial

Website

• Vendor: https://www.juniper.net/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Discussion