CVE-2026-21901: Junos OS and Junos OS Evolved: Configuration of a specific SSH option results in mgd crash

Severity: medium (CVSS 4.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-07-09 · updated 2026-08-26
Weakness: CWE-476

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; * from 23.4 before 23.4R2-S8-EVO. This issue does not affect Junos OS Evolved before 22.3R1-EVO.

Affected products

Juniper Junos OS: 22.3, 22.3-r1-s1, 22.3-r1-s2, 22.3-r2, 22.3-r2-s1, 22.3-r2-s2 (+45)
Juniper Networks Junos OS Evolved: 22.3-r1, 22.3-r1-s1, 22.3-r1-s2, 22.3-r2, 22.3-r2-s1, 22.3-r2-s2 (+47)

References

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