CVE-2026-21901: Junos OS and Junos OS Evolved: Configuration of a specific SSH option results in mgd crash
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 Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Juniper Networks Junos OS / Junos OS Evolvedto a version that resolves this vulnerability.Fixed in 22.3R3-S5 - Upgrade
Upgrade
Juniper Networks Junos OS / Junos OS Evolvedto a version that resolves this vulnerability.Fixed in 22.4R3-S10 - Upgrade
Upgrade
Juniper Networks Junos OS / Junos OS Evolvedto a version that resolves this vulnerability.Fixed in 23.2R2-S7 - Upgrade
Upgrade
Juniper Networks Junos OS / Junos OS Evolvedto a version that resolves this vulnerability.Fixed in 23.4R2-S8 - Upgrade
Upgrade
Juniper Networks Junos OS / Junos OS Evolvedto a version that resolves this vulnerability.Fixed in 24.2R1 - Upgrade
Upgrade
Juniper Networks Junos OS Evolvedto a version that resolves this vulnerability.Fixed in 23.4R2-S8-EVO - Upgrade
Upgrade
Juniper Networks Junos OS Evolvedto a version that resolves this vulnerability.Fixed in 24.2R1-EVO
Event History
Frequently Asked Questions
What is the severity of CVE-2026-21901?
The severity of CVE-2026-21901 is medium with a score of 4.4.
How do I fix CVE-2026-21901?
To fix CVE-2026-21901, ensure that the specific SSH configuration parameter is not set or disabled according to Juniper's recommended practices.
What does CVE-2026-21901 affect?
CVE-2026-21901 affects the management daemon (mgd) in Junos OS and Junos OS Evolved implemented by Juniper Networks.
What is a potential outcome of CVE-2026-21901?
A potential outcome of CVE-2026-21901 is that it can lead to a Denial of Service (DoS) due to a NULL Pointer Dereference.
Who is at risk from CVE-2026-21901?
Local high-privileged users are at risk from CVE-2026-21901 as they can exploit the vulnerability through specific SSH configuration changes.