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CVE-2026-21908: High Vulnerability in Juniper Junos OS

A high-severity Use After Free vulnerability exists in Juniper Networks Junos OS affecting port-based network access control. Organizations should prioritize patching to mitigate potential Denial of Service or arbitrary code execution risks.

HIGHCVSS 7.5 · Published January 15, 2026

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A Use After Free vulnerability was identified in the 802.1X authentication daemon (dot1xd) of Juniper Networks Junos OS and Junos OS Evolved that could allow an authenticated, network-adjacent attacker flapping a port to crash the dot1xd process, leading to a Denial of Service (DoS), or potentially execute arbitrary code within the context of the process running as root. The issue is specific to the processing of a change in authorization (CoA) when a port bounce occurs.

Successful exploitation is outside the attacker's direct control due to the specific timing of the two events required to execute the vulnerable code path. This issue affects systems with 802.1X authentication port-based network access control (PNAC) enabled.

The vulnerability has been scored with a CVSS 4.0 score of 7.5, classified as high severity, indicating a significant risk to organizations that utilize affected versions of Junos OS.

Organizations should prioritize patching immediately.

The vulnerability affects the following versions of Junos OS and Junos OS Evolved:

Junos OS:

* from 23.2R2-S1 before 23.2R2-S5,

* from 23.4R2 before 23.4R2-S6,

* from 24.2 before 24.2R2-S3,

* from 24.4 before 24.4R2-S1,

* from 25.2 before 25.2R1-S2, 25.2R2.

Junos OS Evolved:

* from 23.2R2-S1 before 23.2R2-S5-EVO,

* from 23.4R2 before 23.4R2-S6-EVO,

* from 24.2 before 24.2R2-S3-EVO,

* from 24.4 before 24.4R2-S1-EVO,

* from 25.2 before 25.2R1-S2-EVO, 25.2R2-EVO.

In summary, this vulnerability allows an attacker to potentially disrupt service or execute arbitrary code, which can have severe consequences for network operations.

Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.

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