CVE-2026-21919: Juniper Networks Junos OS · Incorrect Synchronization
Affects Juniper Networks Junos OSSource CVE Database V5
Not known to be exploited · CVSS 6.5 Medium · fixed in 24.4R1-S3 : update Juniper Networks Junos OS when convenient.
Data as of 30 Oct 2026, 06:59 UTC
- EPSS
- 0.2% chance of exploitation in 30 days – higher than 13% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 24.4R1-S3, 24.2R2-S1, 23.4R2-S4 +3
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 9 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
What to do
Upgrade Junos to 24.4R1-S3, 24.2R2-S1 or 23.4R2-S4 (OS); 24.4R1-S3-EVO, 24.2R2-S1-EVO or 23.4R2-S5-EVO (OS Evolved).
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Juniper NetworksJunos OS | Affected
| Fixed in
|
| Juniper NetworksJunos OS Evolved | Affected
| Fixed in
|
AI-suggested
A patch is available for affected Junos OS and Junos OS Evolved versions. Since this is a cloud-hosted service, Juniper Networks manages remediation server-side. Users should verify they are running a fixed version: 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 the system is accessible, hung mgd processes can be manually terminated using CLI commands ('request system process terminate <PID>') or shell commands ('kill -9 <PID>'). Check the vendor advisory for the latest patch and remediation guidance.
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;