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🛡️ CVE-2026-21919 — junos

🟡 CVSS 6.5 — Medium ✅ No Known Exploit CWE-821 NVD
6.5
CVSS Score
0 Low4 Medium7 High9 Critical10

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;

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: Low — an ordinary user account is enough.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-21919 is classified as CWE-821: Incorrect Synchronization. The product utilizes a shared resource in a concurrent manner, but it does not correctly synchronize access to the resource.

Affected software

CVE-2026-21919 is recorded against 2 packages.

  • junos
  • junos-os-evolved

Timeline and source

Published on 9 April 2026 and last revised on 17 June 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

kb.juniper.net

Other advisories for this package

junos has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-821: Incorrect Synchronization) in other software:

Details

Severity MEDIUM
CVSS Score 6.5
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CWE CWE-821
Public Exploit ✅ No
Source NVD
Published 2026-04-09
Updated 2026-08-20
Modified 2026-06-17
Fix URL N/A

Affected Packages

Software From version Fixed in
junos — —
junos-os-evolved — —

References

Mitigation, Vendor Advisory https://kb.juniper.net/JSA106019

Similar Threats

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