Junos OS and Junos OS Evolved: A high frequency of connecting and disconnecting NETCONF sessions causes management unavailability

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;

Timeline

Scores

EPSS (exploitation in 30 days)

0.24% · top 85% of all CVEs (7 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.1.

Weakness

• CWE-821 Incorrect Synchronization (opens in a new tab)All about CWE-821 and its CVEs

Affected products

• Juniper Networks · Junos OS

  • affected 23.4 – < 23.4R2-S4
  • affected 24.2 – < 24.2R2-S1
  • affected 24.4 – < 24.4R1-S3, 24.4R2
  • unaffected all version prior to – < 23.4R1

• Juniper Networks · Junos OS Evolved

  • affected 23.4 – < 23.4R2-S5-EVO
  • affected 24.2 – < 24.2R2-S1-EVO
  • affected 24.4 – < 24.4R1-S3-EVO, 24.4R2-EVO
  • unaffected all version prior to – < 23.4R1-EVO

What to do

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.

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> ]

Exploitation: Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

References (1)

• https://kb.juniper.net/JSA106019 (opens in a new tab)vendor-advisory

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-21919](https://trackcve.app/badge/CVE-2026-21919.svg)](https://trackcve.app/cve/CVE-2026-21919)

Record last updated 13 Apr 2026, 18:06 UTC.