CVE-2026-21901

/// Technical description

A NULL Pointer Dereference vulnerability in the management daemon (mgd) of Juniper Networks Junos OS and Junos OS Evolved allows a local, high-privileged attacker setting or deactivating a specific SSH configuration parameter to create a Denial of Service (DoS).

A local high-privileged user configuring or deactivating a specific 'system services ssh' configuration parameter can exploit a null pointer dereference in one of the functions used by SSH. The function attempts to dereference a null pointer when accessing certain configuration data, resulting in an mgd process crash and restart. Continued execution of these configuration commands will create a sustained Denial of Service (DoS) condition.

This issue affects:

Junos OS:

* from 22.3 before 22.3R3-S5;

* from 22.4 before 22.4R3-S10;

* from 23.2 before 23.2R2-S7;

* from 23.4 before 23.4R2-S8.

This issue does not affect Junos OS before 22.3R1.

Junos OS Evolved:

* from 22.3R1-EVO before 23.2R2-S7-EVO;

* fro

/// 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