CVE-2026-21908

/// Technical description

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. A pointer is freed but was then referenced later in the same code path. 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.

This issue affects:

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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References