CVE-2026-21901

Junos OS and Junos OS Evolved: Configuration of a specific SSH option results in mgd crash

State: Published
Severity: 6.7 Medium
Published: Jul 9, 2026
Updated: Jul 10, 2026
Reserved: Jan 5, 2026

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.

Scores

CVSS	Score	Vector	Source
4.0	6.7 Medium	CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/AU:Y/R:A/V:D/RE:M/U:Green	juniper
3.1	4.4 Medium	CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H	juniper

Weaknesses

CWE-476 NULL Pointer Dereference

Affected Products

Product	Versions
Junos OSJuniper Networks	22.3 to before 22.3R3-S5Affected 22.4 to before 22.4R3-S10Affected 23.2 to before 23.2R2-S7Affected 23.4 to before 23.4R2-S8Affected before 22.3R1Not affected
Junos OS EvolvedJuniper Networks	23.2 to before 23.2R2-S7-EVOAffected 23.4 to before 23.4R2-S8-EVOAffected before 22.3R1-EVONot affected

References

https://github.com/orangecertcc/security-research/security/advisories/GHSA-g4f7-w2rc-hpj6third-party-advisory
https://supportportal.juniper.net/JSA110072vendor-advisory

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