{"id":"CVE-2026-21919","state":"PUBLISHED","title":"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.\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 'show system processes extensive':\n\nuser@host> show system processes extensive | match mgd\n<pid> root         20    0   501M  4640K lockf    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'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. \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;","publishedAt":"2026-04-09T21:26:46.081Z","updatedAt":"2026-04-13T18:06:20.368Z","severity":{"score":7.1,"label":"High","version":"4.0","vector":"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","source":"juniper"},"assigner":"juniper","products":["Juniper Networks Junos OS","Juniper Networks Junos OS Evolved"],"affected":[{"vendor":"Juniper Networks","product":"Junos OS","defaultStatus":"unaffected","versions":[{"version":"23.4","status":"affected","lessThan":"23.4R2-S4","versionType":"semver"},{"version":"24.2","status":"affected","lessThan":"24.2R2-S1","versionType":"semver"},{"version":"24.4","status":"affected","lessThan":"24.4R1-S3, 24.4R2","versionType":"semver"},{"version":"all version prior to","status":"unaffected","lessThan":"23.4R1","versionType":"semver"}]},{"vendor":"Juniper Networks","product":"Junos OS Evolved","defaultStatus":"unaffected","versions":[{"version":"23.4","status":"affected","lessThan":"23.4R2-S5-EVO","versionType":"semver"},{"version":"24.2","status":"affected","lessThan":"24.2R2-S1-EVO","versionType":"semver"},{"version":"24.4","status":"affected","lessThan":"24.4R1-S3-EVO, 24.4R2-EVO","versionType":"semver"},{"version":"all version prior to","status":"unaffected","lessThan":"23.4R1-EVO","versionType":"semver"}]}],"references":["https://kb.juniper.net/JSA106019"],"weaknesses":["CWE-821"],"ingestedAt":"2026-10-29T20:11:10.572Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/21xxx/CVE-2026-21919.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-21919","state":"PUBLISHED","datePublished":"2026-04-09T21:26:46.081Z","dateUpdated":"2026-04-13T18:06:20.368Z","assignerShortName":"juniper","assignerOrgId":"8cbe9d5a-a066-4c94-8978-4b15efeae968","dateReserved":"2026-01-05T17:32:48.711Z"},"containers":{"cna":{"title":"Junos OS and Junos OS Evolved: A high frequency of connecting and disconnecting NETCONF sessions causes management unavailability","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 'show system processes extensive':\n\nuser@host> show system processes extensive | match mgd\n<pid> root         20    0   501M  4640K lockf    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'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. \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;"}],"affected":[{"vendor":"Juniper Networks","product":"Junos OS","defaultStatus":"unaffected","versions":[{"version":"23.4","status":"affected","lessThan":"23.4R2-S4","versionType":"semver"},{"version":"24.2","status":"affected","lessThan":"24.2R2-S1","versionType":"semver"},{"version":"24.4","status":"affected","lessThan":"24.4R1-S3, 24.4R2","versionType":"semver"},{"version":"all version prior to","status":"unaffected","lessThan":"23.4R1","versionType":"semver"}]},{"vendor":"Juniper Networks","product":"Junos OS Evolved","defaultStatus":"unaffected","versions":[{"version":"23.4","status":"affected","lessThan":"23.4R2-S5-EVO","versionType":"semver"},{"version":"24.2","status":"affected","lessThan":"24.2R2-S1-EVO","versionType":"semver"},{"version":"24.4","status":"affected","lessThan":"24.4R1-S3-EVO, 24.4R2-EVO","versionType":"semver"},{"version":"all version prior to","status":"unaffected","lessThan":"23.4R1-EVO","versionType":"semver"}]}],"references":[{"url":"https://kb.juniper.net/JSA106019","tags":["vendor-advisory"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","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","version":"3.1"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]},{"cvssV4_0":{"Automatable":"YES","Recovery":"USER","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"NONE","attackVector":"NETWORK","baseScore":7.1,"baseSeverity":"HIGH","privilegesRequired":"LOW","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","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/AU:Y/R:U/RE:M","version":"4.0","vulnAvailabilityImpact":"HIGH","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnerabilityResponseEffort":"MODERATE"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-821","description":"CWE-821 Incorrect Synchronization","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"juniper","orgId":"8cbe9d5a-a066-4c94-8978-4b15efeae968","dateUpdated":"2026-04-09T21:26:46.081Z"},"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"To be exposed to this issue the device needs to be configured for NETCONF as follows:<br><br><tt>[ system services&nbsp;netconf ... ]</tt>"}],"value":"To be exposed to this issue the device needs to be configured for NETCONF as follows:\n\n[ system services netconf ... ]"}],"datePublic":"2026-04-08T16:00:00.000Z","exploits":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"Juniper SIRT is not aware of any malicious exploitation of this vulnerability."}],"value":"Juniper SIRT is not aware of any malicious exploitation of this vulnerability."}],"solutions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"The following software releases have been updated to resolve this specific issue:<br>Junos OS Evolved: 23.4R2-S5-EVO, 24.2R2-S1-EVO, 24.4R1-S3-EVO, 24.4R2-EVO, 25.2R1-EVO,&nbsp;and all subsequent releases;<br>Junos OS: 23.4R2-S4, 24.2R2-S1, 24.4R1-S3, 24.4R2, 25.2R1, and all subsequent releases."}],"value":"The following software releases have been updated to resolve this specific issue:\nJunos OS Evolved: 23.4R2-S5-EVO, 24.2R2-S1-EVO, 24.4R1-S3-EVO, 24.4R2-EVO, 25.2R1-EVO, and all subsequent releases;\nJunos OS: 23.4R2-S4, 24.2R2-S1, 24.4R1-S3, 24.4R2, 25.2R1, and all subsequent releases."}],"source":{"advisory":"JSA106019","defect":["1866577"],"discovery":"INTERNAL"},"workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"Use access lists or firewall filters to limit access to the device only from trusted hosts and administrators.<br><br>To further reduce the risk of exploitation you can set values as low as needed for your normal operations for:<br><br><tt>[ system services netconf&nbsp;ssh&nbsp;connection-limit &lt;max_connections&gt; ]<br>[ system services netconf ssh&nbsp;rate-limit &lt;connections_per_minute&gt; ]</tt><br>"}],"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 ssh connection-limit <max_connections> ]\n[ system services netconf ssh rate-limit <connections_per_minute> ]"}],"x_generator":{"engine":"Vulnogram 0.1.0-dev"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-21919","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-04-13T17:38:59.428723Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-04-13T18:06:20.368Z"}}]}}}