CVE-2026-21919 (GCVE-0-2026-21919)
Vulnerability from cvelistv5 – Published: 2026-04-09 21:26 – Updated: 2026-04-13 18:06
VLAI
EPSS
VEX
Title
Junos OS and Junos OS Evolved: A high frequency of connecting and disconnecting NETCONF sessions causes management unavailability
Summary
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;
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-04-13 17:38 UTC
CWE
- CWE-821 - Incorrect Synchronization
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://kb.juniper.net/JSA106019 | vendor-advisory |
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Juniper Networks | Junos OS |
Affected:
23.4 , < 23.4R2-S4
(semver)
Affected: 24.2 , < 24.2R2-S1 (semver) Affected: 24.4 , < 24.4R1-S3, 24.4R2 (semver) Unaffected: all version prior to , < 23.4R1 (semver) |
guessed | |
| Juniper Networks | Junos OS Evolved |
Affected:
23.4 , < 23.4R2-S5-EVO
(semver)
Affected: 24.2 , < 24.2R2-S1-EVO (semver) Affected: 24.4 , < 24.4R1-S3-EVO, 24.4R2-EVO (semver) Unaffected: all version prior to , < 23.4R1-EVO (semver) |
guessed |
Date Public
2026-04-08 16:00
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"value": "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.\n\nWhen 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.\n\nThis issue can be monitored by checking for mgd processes in lockf state in the output of \u0027show system processes extensive\u0027:\n\nuser@host\u003e show system processes extensive | match mgd\n\u003cpid\u003e root \u00a0 \u00a0 \u00a0 20 \u00a0 0 501M 4640K lockf \u00a0 1 0:01 0.00% mgd\n\n\nIf the system still can be accessed (either via the CLI or as root, which might still be possible as last resort as this won\u0027t invoke mgd), mgd processes in this state can be killed with \u0027request system process terminate \u003cPID\u003e\u0027 from the CLI or with \u0027kill -9 \u003cPID\u003e\u0027 from the shell.\u00a0\n\n\n\n\nThis issue affects:\n\nJunos OS:\n\n * 23.4 versions before 23.4R2-S4,\n * 24.2 versions before 24.2R2-S1,\n * 24.4 versions before 24.4R1-S3, 24.4R2;\n\n\n\n\nThis issue does not affect Junos OS versions before 23.4R1;\n\n\n\nJunos OS Evolved:\n\n * 23.4 versions before 23.4R2-S5-EVO,\n * 24.2 versions before 24.2R2-S1-EVO,\n * 24.4 versions before 24.4R1-S3-EVO, 24.4R2-EVO.\n\n\n\n\n\n\nThis issue does not affect Junos OS Evolved versions before 23.4R1-EVO;"
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"lang": "es",
"value": "Una vulnerabilidad de sincronizaci\u00f3n incorrecta en el demonio de gesti\u00f3n (mgd) de Juniper Networks Junos OS y Junos OS Evolved permite a un atacante basado en red con privilegios bajos causar una denegaci\u00f3n de servicio (DoS) completa del plano de gesti\u00f3n.\n\nCuando las sesiones NETCONF se establecen y desconectan r\u00e1pidamente, un problema de bloqueo hace que los procesos mgd se cuelguen en un estado inutilizable. Cuando se ha alcanzado el n\u00famero m\u00e1ximo de procesos mgd, no es posible iniciar nuevas sesiones. Esto lleva a la incapacidad de gestionar el dispositivo y requiere un ciclo de encendido para recuperarse.\n\nEste problema se puede monitorear buscando procesos mgd en estado lockf en la salida de \u2019show system processes extensive\u2019:\n\nuser@host\u003e show system processes extensive | match mgd\n[pid] root 20 0 501M 4640K lockf 1 0:01 0.00% mgd\n\nSi a\u00fan se puede acceder al sistema (ya sea a trav\u00e9s de la CLI o como root, lo que a\u00fan podr\u00eda ser posible como \u00faltimo recurso ya que esto no invocar\u00e1 mgd), los procesos mgd en este estado pueden terminarse con \u2019request system process terminate [PID]\u2019 desde la CLI o con \u2019kill -9 [PID]\u2019 desde la shell.\n\nEste problema afecta:\n\nJunos OS:\n\n * versiones 23.4 anteriores a 23.4R2-S4,\n * versiones 24.2 anteriores a 24.2R2-S1,\n * versiones 24.4 anteriores a 24.4R1-S3, 24.4R2;\n\nEste problema no afecta a las versiones de Junos OS anteriores a 23.4R1;\n\nJunos OS Evolved:\n\n * versiones 23.4 anteriores a 23.4R2-S5-EVO,\n * versiones 24.2 anteriores a 24.2R2-S1-EVO,\n * versiones 24.4 anteriores a 24.4R1-S3-EVO, 24.4R2-EVO.\n\nEste problema no afecta a las versiones de Junos OS Evolved anteriores a 23.4R1-EVO;"
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},
"cveMetadata": {
"assignerOrgId": "8cbe9d5a-a066-4c94-8978-4b15efeae968",
"assignerShortName": "juniper",
"cveId": "CVE-2026-21919",
"datePublished": "2026-04-09T21:26:46.081Z",
"dateReserved": "2026-01-05T17:32:48.711Z",
"dateUpdated": "2026-04-13T18:06:20.368Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.