CVE-2026-21919 (GCVE-0-2026-21919)

Vulnerability from cvelistv5 – Published: 2026-04-09 21:26 – Updated: 2026-04-09 21:26
VLAI?
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 ?
6.5 (Medium)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
7.1 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/AU:Y/R:U/RE:M
CWE
  • CWE-821 - Incorrect Synchronization
Assigner
References
Impacted products
Vendor Product Version
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)
Create a notification for this product.
    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)
Create a notification for this product.
Date Public ?
2026-04-08 16:00
Show details on NVD website
To clipboard 

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Junos OS",
          "vendor": "Juniper Networks",
          "versions": [
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              "status": "unaffected",
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              "versionType": "semver"
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          "defaultStatus": "unaffected",
          "product": "Junos OS Evolved",
          "vendor": "Juniper Networks",
          "versions": [
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              "status": "affected",
              "version": "23.4",
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              "status": "affected",
              "version": "24.2",
              "versionType": "semver"
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              "status": "affected",
              "version": "24.4",
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              "status": "unaffected",
              "version": "all version prior to",
              "versionType": "semver"
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      "configurations": [
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          "lang": "en",
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              "type": "text/html",
              "value": "To be exposed to this issue the device needs to be configured for NETCONF as follows:\u003cbr\u003e\u003cbr\u003e\u003ctt\u003e[ system services\u0026nbsp;netconf ... ]\u003c/tt\u003e"
            }
          ],
          "value": "To be exposed to this issue the device needs to be configured for NETCONF as follows:\n\n[ system services\u00a0netconf ... ]"
        }
      ],
      "datePublic": "2026-04-08T16:00:00.000Z",
      "descriptions": [
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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.\u003cbr\u003e\u003cbr\u003eWhen 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.\u003cbr\u003e\u003cbr\u003eThis issue can be monitored by checking for mgd processes in lockf state in the output of \u0027show system processes extensive\u0027:\u003cbr\u003e\u003cbr\u003e\u003ctt\u003euser@host\u0026gt; show system processes extensive | match mgd\u003cbr\u003e\u0026lt;pid\u0026gt; root  \u0026nbsp; \u0026nbsp; \u0026nbsp;  20  \u0026nbsp; 0   501M  4640K lockf  \u0026nbsp; 1   0:01   0.00% mgd\u003c/tt\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\u003cp\u003eIf 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 \u0026lt;PID\u0026gt;\u0027 from the CLI or with \u0027kill -9 \u0026lt;PID\u0026gt;\u0027 from the shell.\u0026nbsp;\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\u003cp\u003eThis issue affects:\u003c/p\u003e\u003cp\u003eJunos OS:\u003c/p\u003e\u003cul\u003e\u003cli\u003e23.4 versions before 23.4R2-S4,\u003c/li\u003e\u003cli\u003e24.2 versions before 24.2R2-S1,\u003c/li\u003e\u003cli\u003e24.4 versions before 24.4R1-S3, 24.4R2;\u003c/li\u003e\u003c/ul\u003e\n\n\u003cp\u003eThis issue does not affect Junos OS versions before 23.4R1;\u003c/p\u003e\n\n\u003cp\u003eJunos OS Evolved:\u003c/p\u003e\u003cul\u003e\u003cli\u003e23.4 versions before 23.4R2-S5-EVO,\u003c/li\u003e\u003cli\u003e24.2 versions before 24.2R2-S1-EVO,\u003c/li\u003e\u003cli\u003e24.4 versions before 24.4R1-S3-EVO, 24.4R2-EVO.\u003c/li\u003e\u003c/ul\u003e\u003cp\u003e\n\n\u003c/p\u003e\u003cp\u003eThis issue does not affect Junos OS Evolved versions before 23.4R1-EVO;\u003c/p\u003e\n\n\n\n\u003cbr\u003e"
            }
          ],
          "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;"
        }
      ],
      "exploits": [
        {
          "lang": "en",
          "supportingMedia": [
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              "type": "text/html",
              "value": "Juniper SIRT is not aware of any malicious exploitation of this vulnerability."
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      "metrics": [
        {
          "cvssV3_1": {
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            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 6.5,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
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            "Safety": "NOT_DEFINED",
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            "providerUrgency": "NOT_DEFINED",
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            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
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            "version": "4.0",
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            "vulnIntegrityImpact": "NONE",
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      "problemTypes": [
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      "providerMetadata": {
        "dateUpdated": "2026-04-09T21:26:46.081Z",
        "orgId": "8cbe9d5a-a066-4c94-8978-4b15efeae968",
        "shortName": "juniper"
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      "source": {
        "advisory": "JSA106019",
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        "discovery": "INTERNAL"
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      "title": "Junos OS and Junos OS Evolved: A high frequency of connecting and disconnecting NETCONF sessions causes management unavailability",
      "workarounds": [
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              "value": "Use access lists or firewall filters to limit access to the device only from trusted hosts and administrators.\u003cbr\u003e\u003cbr\u003eTo further reduce the risk of exploitation you can set values as low as needed for your normal operations for:\u003cbr\u003e\u003cbr\u003e\u003ctt\u003e[ system services netconf\u0026nbsp;ssh\u0026nbsp;connection-limit \u0026lt;max_connections\u0026gt; ]\u003cbr\u003e[ system services netconf ssh\u0026nbsp;rate-limit \u0026lt;connections_per_minute\u0026gt; ]\u003c/tt\u003e\u003cbr\u003e"
            }
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          "value": "Use access lists or firewall filters to limit access to the device only from trusted hosts and administrators.\n\nTo further reduce the risk of exploitation you can set values as low as needed for your normal operations for:\n\n[ system services netconf\u00a0ssh\u00a0connection-limit \u003cmax_connections\u003e ]\n[ system services netconf ssh\u00a0rate-limit \u003cconnections_per_minute\u003e ]"
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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": "2026-04-09T21:26:46.081Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-21919\",\"sourceIdentifier\":\"sirt@juniper.net\",\"published\":\"2026-04-09T22:16:25.173\",\"lastModified\":\"2026-04-09T22:16:25.173\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"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;\"}],\"metrics\":{\"cvssMetricV40\":[{\"source\":\"sirt@juniper.net\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"4.0\",\"vectorString\":\"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:U/V:X/RE:M/U:X\",\"baseScore\":7.1,\"baseSeverity\":\"HIGH\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"attackRequirements\":\"NONE\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"vulnConfidentialityImpact\":\"NONE\",\"vulnIntegrityImpact\":\"NONE\",\"vulnAvailabilityImpact\":\"HIGH\",\"subConfidentialityImpact\":\"NONE\",\"subIntegrityImpact\":\"NONE\",\"subAvailabilityImpact\":\"NONE\",\"exploitMaturity\":\"NOT_DEFINED\",\"confidentialityRequirement\":\"NOT_DEFINED\",\"integrityRequirement\":\"NOT_DEFINED\",\"availabilityRequirement\":\"NOT_DEFINED\",\"modifiedAttackVector\":\"NOT_DEFINED\",\"modifiedAttackComplexity\":\"NOT_DEFINED\",\"modifiedAttackRequirements\":\"NOT_DEFINED\",\"modifiedPrivilegesRequired\":\"NOT_DEFINED\",\"modifiedUserInteraction\":\"NOT_DEFINED\",\"modifiedVulnConfidentialityImpact\":\"NOT_DEFINED\",\"modifiedVulnIntegrityImpact\":\"NOT_DEFINED\",\"modifiedVulnAvailabilityImpact\":\"NOT_DEFINED\",\"modifiedSubConfidentialityImpact\":\"NOT_DEFINED\",\"modifiedSubIntegrityImpact\":\"NOT_DEFINED\",\"modifiedSubAvailabilityImpact\":\"NOT_DEFINED\",\"Safety\":\"NOT_DEFINED\",\"Automatable\":\"YES\",\"Recovery\":\"USER\",\"valueDensity\":\"NOT_DEFINED\",\"vulnerabilityResponseEffort\":\"MODERATE\",\"providerUrgency\":\"NOT_DEFINED\"}}],\"cvssMetricV31\":[{\"source\":\"sirt@juniper.net\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":6.5,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":2.8,\"impactScore\":3.6}]},\"weaknesses\":[{\"source\":\"sirt@juniper.net\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-821\"}]}],\"references\":[{\"url\":\"https://kb.juniper.net/JSA106019\",\"source\":\"sirt@juniper.net\"}]}}"
  }
}


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Sightings

Author Source Type Date

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.



Detection rules are retrieved from Rulezet.