CVE-2026-21901

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;