{"id":"CVE-2026-21910","state":"PUBLISHED","title":"Junos OS: EX4k Series, QFX5k Series: In an EVPN-VXLAN configuration link flaps cause Inter-VNI traffic drop","description":"An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (PFE) of Juniper Networks Junos OS on EX4k Series and QFX5k Series platforms allows an unauthenticated network-adjacent attacker flapping an interface to cause traffic between VXLAN Network Identifiers (VNIs) to drop, leading to a Denial of Service (DoS).\n\nOn all EX4k and QFX5k platforms, a link flap in an\n\nEVPN-VXLAN configuration Link Aggregation Group (LAG)\nresults in Inter-VNI traffic dropping when there are multiple load-balanced next-hop routes for the same destination.\n\nThis issue is only applicable to systems that support EVPN-VXLAN Virtual Port-Link Aggregation Groups (VPLAG), such as the QFX5110, QFX5120, QFX5200, EX4100, EX4300, EX4400, and EX4650.\n\nService can only be restored by restarting the affected FPC via the 'request chassis fpc restart slot <slot-number>' command.\n\nThis issue affects Junos OS \n\non EX4k and QFX5k Series: \n\n\n\n  *  all versions before 21.4R3-S12, \n  *  all versions of 22.2\n  *  from 22.4 before 22.4R3-S8, \n  *  from 23.2 before 23.2R2-S5, \n  *  from 23.4 before 23.4R2-S5, \n  *  from 24.2 before 24.2R2-S3,\n  *  from 24.4 before 24.4R2.","publishedAt":"2026-01-15T20:23:29.682Z","updatedAt":"2026-01-15T20:51:57.933Z","severity":{"score":7.1,"label":"High","version":"4.0","vector":"CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:U/RE:M/U:Green","source":"juniper"},"assigner":"juniper","products":["Juniper Networks Junos OS"],"affected":[{"vendor":"Juniper Networks","product":"Junos OS","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThan":"21.4R3-S12","versionType":"semver"},{"version":"22.2","status":"affected","lessThan":"22.2*","versionType":"semver"},{"version":"22.4","status":"affected","lessThan":"22.4R3-S8","versionType":"semver"},{"version":"23.2","status":"affected","lessThan":"23.2R2-S5","versionType":"semver"},{"version":"23.4","status":"affected","lessThan":"23.4R2-S5","versionType":"semver"},{"version":"24.2","status":"affected","lessThan":"24.2R2-S3","versionType":"semver"},{"version":"24.4","status":"affected","lessThan":"24.4R2","versionType":"semver"}],"platforms":["EX4k Series","QFX5k Series"]}],"references":["https://supportportal.juniper.net/JSA106009","https://kb.juniper.net/JSA106009"],"weaknesses":["CWE-754"],"ingestedAt":"2026-10-29T20:11:10.572Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/21xxx/CVE-2026-21910.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-21910","state":"PUBLISHED","datePublished":"2026-01-15T20:23:29.682Z","dateUpdated":"2026-01-15T20:51:57.933Z","assignerShortName":"juniper","assignerOrgId":"8cbe9d5a-a066-4c94-8978-4b15efeae968","dateReserved":"2026-01-05T17:32:48.710Z"},"containers":{"cna":{"title":"Junos OS: EX4k Series, QFX5k Series: In an EVPN-VXLAN configuration link flaps cause Inter-VNI traffic drop","descriptions":[{"lang":"en","value":"An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (PFE) of Juniper Networks Junos OS on EX4k Series and QFX5k Series platforms allows an unauthenticated network-adjacent attacker flapping an interface to cause traffic between VXLAN Network Identifiers (VNIs) to drop, leading to a Denial of Service (DoS).\n\nOn all EX4k and QFX5k platforms, a link flap in an\n\nEVPN-VXLAN configuration Link Aggregation Group (LAG)\nresults in Inter-VNI traffic dropping when there are multiple load-balanced next-hop routes for the same destination.\n\nThis issue is only applicable to systems that support EVPN-VXLAN Virtual Port-Link Aggregation Groups (VPLAG), such as the QFX5110, QFX5120, QFX5200, EX4100, EX4300, EX4400, and EX4650.\n\nService can only be restored by restarting the affected FPC via the 'request chassis fpc restart slot <slot-number>' command.\n\nThis issue affects Junos OS \n\non EX4k and QFX5k Series: \n\n\n\n  *  all versions before 21.4R3-S12, \n  *  all versions of 22.2\n  *  from 22.4 before 22.4R3-S8, \n  *  from 23.2 before 23.2R2-S5, \n  *  from 23.4 before 23.4R2-S5, \n  *  from 24.2 before 24.2R2-S3,\n  *  from 24.4 before 24.4R2."}],"affected":[{"vendor":"Juniper Networks","product":"Junos OS","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThan":"21.4R3-S12","versionType":"semver"},{"version":"22.2","status":"affected","lessThan":"22.2*","versionType":"semver"},{"version":"22.4","status":"affected","lessThan":"22.4R3-S8","versionType":"semver"},{"version":"23.2","status":"affected","lessThan":"23.2R2-S5","versionType":"semver"},{"version":"23.4","status":"affected","lessThan":"23.4R2-S5","versionType":"semver"},{"version":"24.2","status":"affected","lessThan":"24.2R2-S3","versionType":"semver"},{"version":"24.4","status":"affected","lessThan":"24.4R2","versionType":"semver"}],"platforms":["EX4k Series","QFX5k Series"]}],"references":[{"url":"https://supportportal.juniper.net/JSA106009","tags":["vendor-advisory"]},{"url":"https://kb.juniper.net/JSA106009","tags":["vendor-advisory"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"ADJACENT_NETWORK","availabilityImpact":"HIGH","baseScore":6.5,"baseSeverity":"MEDIUM","confidentialityImpact":"NONE","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:A/AC:L/PR:N/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":"ADJACENT","baseScore":7.1,"baseSeverity":"HIGH","privilegesRequired":"NONE","providerUrgency":"GREEN","subAvailabilityImpact":"LOW","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:U/RE:M/U:Green","version":"4.0","vulnAvailabilityImpact":"HIGH","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnerabilityResponseEffort":"MODERATE"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-754","description":"CWE-754 Improper Check for Unusual or Exceptional Conditions","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"juniper","orgId":"8cbe9d5a-a066-4c94-8978-4b15efeae968","dateUpdated":"2026-01-15T20:23:29.682Z"},"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"This issue requires the following configuration:<br><br>\n\n<tt><span style=\"background-color: rgb(255, 255, 255);\">[interfaces &lt;if&gt; ether-options 802.3ad ae0]</span><br>[interfaces ae0 aggregated-ether-options lacp]<br></tt><br><tt><tt>[protocols bgp group &lt;name&gt; family evpn signaling]<br></tt>[protocols evpn encapsulation vxlan]</tt>"}],"value":"This issue requires the following configuration:\n\n\n\n[interfaces <if> ether-options 802.3ad ae0]\n[interfaces ae0 aggregated-ether-options lacp]\n\n[protocols bgp group <name> family evpn signaling]\n[protocols evpn encapsulation vxlan]"}],"datePublic":"2026-01-14T17:00:00.000Z","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: Junos OS 21.4R3-S12, 22.4R3-S8, 23.2R2-S5, 23.4R2-S5, 24.2R2-S3, 24.4R2, 25.2R1, and all subsequent releases."}],"value":"The following software releases have been updated to resolve this specific issue: Junos OS 21.4R3-S12, 22.4R3-S8, 23.2R2-S5, 23.4R2-S5, 24.2R2-S3, 24.4R2, 25.2R1, and all subsequent releases."}],"source":{"advisory":"JSA106009","defect":["1847849"],"discovery":"USER"},"workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"There are no known workarounds for this issue."}],"value":"There are no known workarounds for this issue."}],"x_generator":{"engine":"Vulnogram 0.1.0-dev"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-01-15T20:51:52.841479Z","id":"CVE-2026-21910","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-01-15T20:51:57.933Z"}}]}}}