Description
An Incorrect Synchronization vulnerability in the management daemon (mgd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker with low privileges to cause a complete Denial-of-Service (DoS) of the management plane.

When NETCONF sessions are quickly established and disconnected, a locking issue causes mgd processes to hang in an unusable state. When the maximum number of mgd processes has been reached, no new logins are possible. This leads to the inability to manage the device and requires a power-cycle to recover.

This issue can be monitored by checking for mgd processes in lockf state in the output of 'show system processes extensive':

user@host> show system processes extensive | match mgd
<pid> root       20   0 501M 4640K lockf   1 0:01 0.00% mgd


If the system still can be accessed (either via the CLI or as root, which might still be possible as last resort as this won't invoke mgd), mgd processes in this state can be killed with 'request system process terminate <PID>' from the CLI or with 'kill -9 <PID>' from the shell. 




This issue affects:

Junos OS:

* 23.4 versions before 23.4R2-S4,
* 24.2 versions before 24.2R2-S1,
* 24.4 versions before 24.4R1-S3, 24.4R2;




This issue does not affect Junos OS versions before 23.4R1;



Junos OS Evolved:

* 23.4 versions before 23.4R2-S5-EVO,
* 24.2 versions before 24.2R2-S1-EVO,
* 24.4 versions before 24.4R1-S3-EVO, 24.4R2-EVO.






This issue does not affect Junos OS Evolved versions before 23.4R1-EVO;
Published: 2026-04-09
Score: 7.1 High
EPSS: n/a
KEV: No
Impact: Denial of Service on management plane
Action: Patch Immediately
AI Analysis

Impact

An incorrect synchronization bug in the Juniper Networks Junos OS and Junos OS Evolved management daemon (mgd) allows a low‑privilege network attacker to repeatedly connect and disconnect NETCONF sessions. The rapid session churn triggers a locking issue that causes mgd processes to hang in a lockf state. When all mgd processes are occupied, new management logons fail and the device becomes unmanageable, requiring a power cycle to recover.

Affected Systems

The flaw affects Juniper Networks Junos OS and Junos OS Evolved on versions prior to 23.4R2-S4, 24.2R2-S1, 24.4R1-S3 and 24.4R2, as well as the corresponding Evolved releases before 23.4R2-S5-EVO, 24.2R2-S1-EVO, 24.4R1-S3-EVO and 24.4R2-EVO. Versions before 23.4R1 for either family are not impacted.

Risk and Exploitability

The vulnerability carries a CVSS score of 7.1, indicating a high severity. Exploitation requires only network access and low privileges on the device, making the attack vector likely to be initiated from inside the network or from compromised hosts with modest credentials. Because EPSS data is unavailable and the issue is not listed in the KEV catalog, the market exploitation probability is uncertain, but the high CVSS and straightforward operational conditions suggest that the risk to environments with exposed NETCONF interfaces is significant.

Generated by OpenCVE AI on April 9, 2026 at 22:27 UTC.

Remediation

Vendor Solution

The following software releases have been updated to resolve this specific issue: Junos OS Evolved: 23.4R2-S5-EVO, 24.2R2-S1-EVO, 24.4R1-S3-EVO, 24.4R2-EVO, 25.2R1-EVO, and all subsequent releases; Junos OS: 23.4R2-S4, 24.2R2-S1, 24.4R1-S3, 24.4R2, 25.2R1, and all subsequent releases.

Vendor Workaround

Use access lists or firewall filters to limit access to the device only from trusted hosts and administrators. To further reduce the risk of exploitation you can set values as low as needed for your normal operations for: [ system services netconf ssh connection-limit <max_connections> ] [ system services netconf ssh rate-limit <connections_per_minute> ]

OpenCVE Recommended Actions

  • Apply the latest Junos OS or Junos OS Evolved patch version as listed in the vendor’s solution.
  • Restrict device access to trusted hosts using access lists or firewall filters.
  • Configure the maximum number of concurrent NETCONF SSH connections with 'system services netconf ssh connection-limit <max_connections>' to reduce load.
  • Limit the rate of NETCONF session establishment with 'system services netconf ssh rate-limit <connections_per_minute>'.
  • Monitor mgd processes for the lockf state and terminate any stuck processes with 'request system process terminate <PID>' or 'kill -9 <PID>' if the device remains reachable.

Generated by OpenCVE AI on April 9, 2026 at 22:27 UTC.

Tracking

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Advisories

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References
Link Providers
https://kb.juniper.net/JSA106019 cve-icon cve-icon
History

Fri, 10 Apr 2026 09:00:00 +0000

Type Values Removed Values Added
First Time appeared Juniper Networks
Juniper Networks junos Os
Juniper Networks junos Os Evolved
Vendors & Products Juniper Networks
Juniper Networks junos Os
Juniper Networks junos Os Evolved

Thu, 09 Apr 2026 21:45:00 +0000

Type Values Removed Values Added
Description An Incorrect Synchronization vulnerability in the management daemon (mgd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker with low privileges to cause a complete Denial-of-Service (DoS) of the management plane. When NETCONF sessions are quickly established and disconnected, a locking issue causes mgd processes to hang in an unusable state. When the maximum number of mgd processes has been reached, no new logins are possible. This leads to the inability to manage the device and requires a power-cycle to recover. This issue can be monitored by checking for mgd processes in lockf state in the output of 'show system processes extensive': user@host> show system processes extensive | match mgd <pid> root       20   0 501M 4640K lockf   1 0:01 0.00% mgd If the system still can be accessed (either via the CLI or as root, which might still be possible as last resort as this won't invoke mgd), mgd processes in this state can be killed with 'request system process terminate <PID>' from the CLI or with 'kill -9 <PID>' from the shell.  This issue affects: Junos OS: * 23.4 versions before 23.4R2-S4, * 24.2 versions before 24.2R2-S1, * 24.4 versions before 24.4R1-S3, 24.4R2; This issue does not affect Junos OS versions before 23.4R1; Junos OS Evolved: * 23.4 versions before 23.4R2-S5-EVO, * 24.2 versions before 24.2R2-S1-EVO, * 24.4 versions before 24.4R1-S3-EVO, 24.4R2-EVO. This issue does not affect Junos OS Evolved versions before 23.4R1-EVO;
Title Junos OS and Junos OS Evolved: A high frequency of connecting and disconnecting NETCONF sessions causes management unavailability
Weaknesses CWE-821
References
Metrics cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

cvssV4_0

{'score': 7.1, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/AU:Y/R:U/RE:M'}

Subscriptions

Juniper Networks Junos Os Junos Os Evolved
cve-icon MITRE

Status: PUBLISHED

Assigner: juniper

Published:

Updated: 2026-04-09T21:26:46.081Z

Reserved: 2026-01-05T17:32:48.711Z

Link: CVE-2026-21919

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-04-09T22:16:25.173

Modified: 2026-04-09T22:16:25.173

Link: CVE-2026-21919

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-04-10T09:28:45Z

Weaknesses