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IS-IS must be enabled on a broadcast (LAN) interface AND there should be an active IS-IS adjacency on that interface:

switch(config-router-isis)#show active\nrouter isis 1\n   net 49.0001.1111.1111.1001.00\nswitch(config-if-Et1)#show active\ninterface Ethernet1\n   isis enable 1

switch#show isis interface detail\nIS-IS Instance: 1 VRF: default\n
\n  Interface Ethernet1:\n    Index: 4 SNPA: 2:2:0:1:0:0\n    MTU: 1497 Type: broadcast\n    Supported address families: IPv4, IPv6\n    Area proxy boundary is disabled\n    BFD IPv4 is disabled\n    BFD IPv6 is disabled\n    Hello padding is enabled\n    Level 1:\n      Metric: 10, Number of adjacencies: 1\n      LAN-ID: 1111.1111.1001.04, Priority: 64\n      DIS: 1111.1111.1001, DIS priority: 64\n      Authentication mode: None\n      TI-LFA protection is disabled for IPv4\n      TI-LFA protection is disabled for IPv6\n    Adjacency 1111.1111.1002:\n      State: UP, Level: 1 Type: Level 1 IS\n      Advertised hold time: 9\n      Neighbor supported address families: IPv4, IPv6\n      Address family match: Enabled\n      SNPA: 2:2:0:2:0:0, Priority: 64\n      IPv4 interface address: 10.0.0.2\n      IPv6 interface address: fe80::2:ff:fe02:0\n      Area addresses: 49.0001

If IS-IS is not configured OR IS-IS is configured only on point-to-point interfaces, there is no exposure to this issue.

switch#show isis interface detail\nIS-IS Instance: 1 VRF: default\n \n  Interface Ethernet1:\n    Index: 4 SNPA: P2P\n    MTU: 1497 Type: point-to-point\n    Supported address families: IPv4, IPv6\n    Area proxy boundary is disabled\n    BFD IPv4 is disabled\n    BFD IPv6 is disabled\n    Hello padding is enabled\n    Local fast flooding is disabled\n    Level 1:\n      Metric: 10, Number of adjacencies: 1\n      Link-ID: 04\n      Authentication mode: None\n      TI-LFA protection is disabled for IPv4\n      TI-LFA protection is disabled for IPv6\n    Adjacency 1111.1111.1002:\n      State: UP, Level: 1 Type: Level 1 IS\n      Advertised hold time: 30\n      Neighbor supported address families: IPv4, IPv6\n      Address family match: Enabled\n      IPv4 interface address: 1.0.0.2\n      IPv6 interface address: fe80::2:ff:fe02:0\n      Area addresses: 49.0001\n      Peer fast flooding is disabled
"}],"value":"IS-IS must be enabled on a broadcast (LAN) interface AND there should be an active IS-IS adjacency on that interface:\n\n\n\nswitch(config-router-isis)#show active\nrouter isis 1\n   net 49.0001.1111.1111.1001.00\nswitch(config-if-Et1)#show active\ninterface Ethernet1\n   isis enable 1\n\n\n\nswitch#show isis interface detail\nIS-IS Instance: 1 VRF: default\n\n\n  Interface Ethernet1:\n    Index: 4 SNPA: 2:2:0:1:0:0\n    MTU: 1497 Type: broadcast\n    Supported address families: IPv4, IPv6\n    Area proxy boundary is disabled\n    BFD IPv4 is disabled\n    BFD IPv6 is disabled\n    Hello padding is enabled\n    Level 1:\n      Metric: 10, Number of adjacencies: 1\n      LAN-ID: 1111.1111.1001.04, Priority: 64\n      DIS: 1111.1111.1001, DIS priority: 64\n      Authentication mode: None\n      TI-LFA protection is disabled for IPv4\n      TI-LFA protection is disabled for IPv6\n    Adjacency 1111.1111.1002:\n      State: UP, Level: 1 Type: Level 1 IS\n      Advertised hold time: 9\n      Neighbor supported address families: IPv4, IPv6\n      Address family match: Enabled\n      SNPA: 2:2:0:2:0:0, Priority: 64\n      IPv4 interface address: 10.0.0.2\n      IPv6 interface address: fe80::2:ff:fe02:0\n      Area addresses: 49.0001\n\n\n\n\n\nIf IS-IS is not configured OR IS-IS is configured only on point-to-point interfaces, there is no exposure to this issue.\n\n\n\n\n\nswitch#show isis interface detail\nIS-IS Instance: 1 VRF: default\n \n  Interface Ethernet1:\n    Index: 4 SNPA: P2P\n    MTU: 1497 Type: point-to-point\n    Supported address families: IPv4, IPv6\n    Area proxy boundary is disabled\n    BFD IPv4 is disabled\n    BFD IPv6 is disabled\n    Hello padding is enabled\n    Local fast flooding is disabled\n    Level 1:\n      Metric: 10, Number of adjacencies: 1\n      Link-ID: 04\n      Authentication mode: None\n      TI-LFA protection is disabled for IPv4\n      TI-LFA protection is disabled for IPv6\n    Adjacency 1111.1111.1002:\n      State: UP, Level: 1 Type: Level 1 IS\n      Advertised hold time: 30\n      Neighbor supported address families: IPv4, IPv6\n      Address family match: Enabled\n      IPv4 interface address: 1.0.0.2\n      IPv6 interface address: fe80::2:ff:fe02:0\n      Area addresses: 49.0001\n      Peer fast flooding is disabled"}],"credits":[{"lang":"en","type":"finder","value":"This issue was discovered internally by Arista and the company is not aware of any malicious uses of these issues in customer networks."}],"descriptions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

On affected platforms running Arista EOS with IS-IS configured on a broadcast interface, an unauthenticated attacker can send a crafted IS-IS Hello Protocol Data Unit (PDU) that causes the device to tear down an established IS-IS adjacency. This may result in traffic disruption and loss of IP reachability for prefixes advertised through that adjacency.

"}],"value":"On affected platforms running Arista EOS with IS-IS configured on a broadcast interface, an unauthenticated attacker can send a crafted IS-IS Hello Protocol Data Unit (PDU) that causes the device to tear down an established IS-IS adjacency. This may result in traffic disruption and loss of IP reachability for prefixes advertised through that adjacency."}],"impacts":[{"capecId":"CAPEC-272","descriptions":[{"lang":"en","value":"CAPEC-272 Protocol Manipulation"}]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"ADJACENT_NETWORK","availabilityImpact":"HIGH","baseScore":7.4,"baseSeverity":"HIGH","confidentialityImpact":"NONE","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"CHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H","version":"3.1"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]},{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"ADJACENT","baseScore":7,"baseSeverity":"HIGH","exploitMaturity":"NOT_DEFINED","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H","version":"4.0","vulnAvailabilityImpact":"HIGH","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-696","description":"CWE-696: Incorrect Behavior Order","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-09-15T23:08:19.771Z","orgId":"c8b34d1a-69ae-45c3-88fe-f3b3d44f39b7","shortName":"Arista"},"references":[{"name":"Security Advisory 0160","tags":["vendor-advisory"],"url":"https://www.arista.com/en/support/advisories-notices/security-advisory/24716-security-advisory-0160"}],"solutions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

The recommended resolution is to upgrade to a fixed software version.

"}],"value":"The recommended resolution is to upgrade to a fixed software version."}],"source":{"advisory":"0160","defects":["BUG1840504"],"discovery":"UNKNOWN"},"title":"Security Advisory 0160","workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

No workaround is available for this issue.

"}],"value":"No workaround is available for this issue."}],"x_generator":{"engine":"Vulnogram 1.0.5"}}},"cveMetadata":{"assignerOrgId":"c8b34d1a-69ae-45c3-88fe-f3b3d44f39b7","assignerShortName":"Arista","cveId":"CVE-2026-73446","datePublished":"2026-09-15T23:08:19.771Z","dateReserved":"2026-08-12T16:42:47.920Z","dateUpdated":"2026-09-16T19:34:18.384Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-09-16 00:17:05","lastModifiedDate":"2026-09-16 20:17:26","problem_types":["CWE-696","CWE-696 CWE-696: Incorrect Behavior Order"],"metrics":{"cvssMetricV40":[{"source":"psirt@arista.com","type":"Secondary","cvssData":{"version":"4.0","vectorString":"CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/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:X/R:X/V:X/RE:X/U:X","baseScore":7,"baseSeverity":"HIGH","attackVector":"ADJACENT","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"HIGH","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":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}}],"cvssMetricV31":[{"source":"psirt@arista.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H","baseScore":7.4,"baseSeverity":"HIGH","attackVector":"ADJACENT_NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"CHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"},"exploitabilityScore":2.8,"impactScore":4}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-09-16T19:34:09.117613Z","id":"CVE-2026-73446","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"73446","Ordinal":"1","Title":"Security Advisory 0160","CVE":"CVE-2026-73446","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"73446","Ordinal":"1","NoteData":"On affected platforms running Arista EOS with IS-IS configured on a broadcast interface, an unauthenticated attacker can send a crafted IS-IS Hello Protocol Data Unit (PDU) that causes the device to tear down an established IS-IS adjacency. This may result in traffic disruption and loss of IP reachability for prefixes advertised through that adjacency.","Type":"Description","Title":"Security Advisory 0160"}]}}}