CVE-2026-21919: CWE-821 Incorrect Synchronization in Juniper Networks Junos OS
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;
AI Analysis
Technical Summary
This vulnerability (CVE-2026-21919) involves incorrect synchronization in the mgd process of Juniper Networks Junos OS and Junos OS Evolved. The issue arises when NETCONF sessions are rapidly created and disconnected, causing mgd processes to hang in a lockf state. Once the maximum number of mgd processes is reached, no new management logins can be established, resulting in a denial-of-service condition for device management. Affected versions include Junos OS 23.4 prior to 23.4R2-S4, 24.2 prior to 24.2R2-S1, and 24.4 prior to 24.4R1-S3 and 24.4R2, as well as corresponding Junos OS Evolved versions. The vulnerability does not affect versions before 23.4R1 or 23.4R1-EVO. The vendor provides patches and manages remediation for this cloud-hosted service.
Potential Impact
An attacker with low privileges can cause a complete denial-of-service of the management plane by exploiting this synchronization flaw, preventing new management logins and requiring a power-cycle to restore device management functionality. There is no impact on confidentiality or integrity, only availability is affected.
Mitigation Recommendations
A patch is available for affected Junos OS and Junos OS Evolved versions. Since this is a cloud service, Juniper Networks manages remediation server-side. Users should verify that their devices are running patched versions: 23.4R2-S4 or later for 23.4, 24.2R2-S1 or later for 24.2, and 24.4R1-S3 or later for 24.4 releases. If unpatched and the system is accessible, mgd processes in lockf state can be manually terminated via CLI or shell commands as a temporary workaround.
CVE-2026-21919: CWE-821 Incorrect Synchronization in Juniper Networks Junos OS
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;
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CVE-2026-21919) involves incorrect synchronization in the mgd process of Juniper Networks Junos OS and Junos OS Evolved. The issue arises when NETCONF sessions are rapidly created and disconnected, causing mgd processes to hang in a lockf state. Once the maximum number of mgd processes is reached, no new management logins can be established, resulting in a denial-of-service condition for device management. Affected versions include Junos OS 23.4 prior to 23.4R2-S4, 24.2 prior to 24.2R2-S1, and 24.4 prior to 24.4R1-S3 and 24.4R2, as well as corresponding Junos OS Evolved versions. The vulnerability does not affect versions before 23.4R1 or 23.4R1-EVO. The vendor provides patches and manages remediation for this cloud-hosted service.
Potential Impact
An attacker with low privileges can cause a complete denial-of-service of the management plane by exploiting this synchronization flaw, preventing new management logins and requiring a power-cycle to restore device management functionality. There is no impact on confidentiality or integrity, only availability is affected.
Mitigation Recommendations
A patch is available for affected Junos OS and Junos OS Evolved versions. Since this is a cloud service, Juniper Networks manages remediation server-side. Users should verify that their devices are running patched versions: 23.4R2-S4 or later for 23.4, 24.2R2-S1 or later for 24.2, and 24.4R1-S3 or later for 24.4 releases. If unpatched and the system is accessible, mgd processes in lockf state can be manually terminated via CLI or shell commands as a temporary workaround.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- juniper
- Date Reserved
- 2026-01-05T17:32:48.711Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
- Is Cloud Service
- true
Threat ID: 69d843721cc7ad14da3fb400
Added to database: 4/10/2026, 12:25:22 AM
Last enriched: 4/10/2026, 12:52:04 AM
Last updated: 4/10/2026, 8:14:26 AM
Views: 4
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