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

Description (CNA)

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 (CNA)

Vendor / product	Versions
Juniper Networks / Junos OS	affected 22.3 before 22.3R3-S5; affected 22.4 before 22.4R3-S10; affected 23.2 before 23.2R2-S7; affected 23.4 before 23.4R2-S8; unaffected 0 before 22.3R1
Juniper Networks / Junos OS Evolved	affected 23.2 before 23.2R2-S7-EVO; affected 23.4 before 23.4R2-S8-EVO; unaffected 0 before 22.3R1-EVO

CWE

CWE-476

References

ADP enrichment

CISA-ADP

No English description supplied.

https://github.com/orangecertcc/security-research/security/advisories/GHSA-g4f7-w2rc-hpj6