Juniper Junos OS/Junos OS Evolved Management Daemon incorrect synchronization

Summaryinfo

A vulnerability labeled as critical has been found in Juniper Junos OS and Junos OS Evolved. Affected by this vulnerability is an unknown functionality of the component Management Daemon. The manipulation results in incorrect synchronization. This vulnerability is known as CVE-2026-21919. It is possible to launch the attack remotely. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Juniper Junos OS and Junos OS Evolved (the affected version unknown). It has been classified as critical. Affected is an unknown part of the component Management Daemon. The manipulation with an unknown input leads to a incorrect synchronization vulnerability. CWE is classifying the issue as CWE-821. The product utilizes a shared resource in a concurrent manner, but it does not correctly synchronize access to the resource. This is going to have an impact on availability. CVE summarizes:

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 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 ' from the CLI or with 'kill -9 ' 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;

The advisory is available at kb.juniper.net. This vulnerability is traded as CVE-2026-21919 since 01/05/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The technical details are unknown and an exploit is not available. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 04/10/2026).

Upgrading eliminates this vulnerability.

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Type

• Router Operating System

Vendor

• Juniper

Name

• Junos OS
• Junos OS Evolved

License

• commercial

Website

• Vendor: https://www.juniper.net/

CPE 2.3info

• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Discussion