{
  "document": {
    "acknowledgments": [
      {
        "summary": "This vulnerability was found during internal security testing."
      }
    ],
    "category": "csaf_security_advisory",
    "csaf_version": "2.0",
    "notes": [
      {
        "category": "summary",
        "text": "A vulnerability in the Intermediate System-to-Intermediate System (IS-IS) multi-instance routing feature of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause the IS-IS process to restart unexpectedly.\r\n\r\nThis vulnerability is due to insufficient input validation of ingress IS-IS packets. An attacker could exploit this vulnerability by sending crafted IS-IS packets to an affected device after forming an adjacency. A successful exploit could allow the attacker to cause the IS-IS process to restart unexpectedly, resulting in a temporary loss of connectivity to advertised networks and a denial of service (DoS) condition.\r\n\r\nNote: The IS-IS protocol is a routing protocol. To exploit this vulnerability, an attacker must be Layer 2-adjacent to the affected device and must have formed an adjacency.\r\n\r\nCisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.\r\n\r\n\r\n\r\nThis advisory is part of the March 2026 release of the Cisco IOS XR Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: March 2026 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication [\"https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-75772\"].",
        "title": "Summary"
      },
      {
        "category": "general",
        "text": "This vulnerability affects Cisco devices if they are running a vulnerable release of Cisco IOS XR Software and have the IS-IS multi-instance routing feature enabled.\r\n\r\nFor information about which Cisco software releases are vulnerable, see the Fixed Software [\"#fs\"] section of this advisory.\r\n\r\nDetermine Whether the Device Has a Vulnerable Configuration\r\n\r\nTo determine whether a device is configured for IS-IS multi-instance routing, use the show running-config router isis | include instance-id EXEC CLI command. If the command returns at least one instance-id, the device is configured for IS-IS multi-instance routing and is affected by this vulnerability, as shown in the following example:\r\n\r\n\r\nRP/0/RP0/CPU0:ios#show running-config router isis | include instance-id\r\nMon Feb  9 17:30:18.448 UTC\r\ninstance-id 1\r\nRP/0/RP0/CPU0:ios#\r\n\r\nIf the command returns no output, the device is not affected by this vulnerability.",
        "title": "Vulnerable Products"
      },
      {
        "category": "general",
        "text": "Only products listed in the Vulnerable Products [\"#vp\"] section of this advisory are known to be affected by this vulnerability.\r\n\r\nCisco has confirmed that this vulnerability does not affect the following Cisco products:\r\n\r\nIOS Software\r\nIOS XE Software\r\nNX-OS Software",
        "title": "Products Confirmed Not Vulnerable"
      },
      {
        "category": "general",
        "text": "There are no workarounds that address this vulnerability.\r\n\r\nAs a mitigation, configure IS-IS area authentication. This would require an attacker to authenticate successfully to the IS-IS area before they are able to form an adjacency and exploit this vulnerability. For more information on configuring IS-IS authentication, see the IS-IS Authentication [\"https://www.cisco.com/c/en/us/td/docs/iosxr/ncs5500/routing/24xx/configuration/guide/b-routing-cg-ncs5500-24xx/implementing-isis.html#con_1276647\"] section of the Routing Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 24.1.x, 24.2.x, 24.3.x, 24.4.x.\r\n\r\nWhile this mitigation has been deployed and was proven successful in a test environment, customers should determine the applicability and effectiveness in their own environment and under their own use conditions. Customers should be aware that any mitigation that is implemented may negatively impact the functionality or performance of their network based on intrinsic customer deployment scenarios and limitations. Customers should not deploy any mitigations before first evaluating the applicability to their own environment and any impact to such environment.",
        "title": "Workarounds"
      },
      {
        "category": "general",
        "text": "Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To fully remediate this vulnerability and avoid future exposure as described in this advisory, Cisco strongly recommends that customers upgrade to the fixed software indicated in this advisory.\r\n      Fixed Releases\r\nIn the following table, the left column lists Cisco software releases or trains. The right column indicates whether a release (train) is affected by the vulnerability that is described in this advisory and the first release that includes the fix for this vulnerability.\r\n          Cisco IOS XR Software Release  First Fixed Release          7.7 and earlier  Not affected.      7.8  Migrate to a fixed release.      7.9  Migrate to a fixed release.      7.10   Migrate to a fixed release.      7.11   Migrate to a fixed release.      24.1  Migrate to a fixed release.      24.2  Migrate to a fixed release.      24.3  Migrate to a fixed release.      24.4  Migrate to a fixed release.      25.1  Migrate to a fixed release.      25.2  25.2.2      25.3  25.3.1      25.4  Not affected.\r\n\r\nSMUs are also available to address this vulnerability. Customers who require SMUs for platforms or releases that are not available are advised to contact their support organization. For more information on finding which SMUs may have been published for this vulnerability, see the Download section of Understand Cisco IOS XR Software Maintenance Updates (SMUs) [\"https://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-xr-software/116332-maintain-ios-xr-smu-00.html#toc-hId-972485609\"].\r\n\r\nThe Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.",
        "title": "Fixed Software"
      },
      {
        "category": "general",
        "text": "To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy [\"http://www.cisco.com/web/about/security/psirt/security_vulnerability_policy.html\"]. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.",
        "title": "Vulnerability Policy"
      },
      {
        "category": "general",
        "text": "The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.",
        "title": "Exploitation and Public Announcements"
      },
      {
        "category": "general",
        "text": "This vulnerability was found during internal security testing.",
        "title": "Source"
      },
      {
        "category": "legal_disclaimer",
        "text": "SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT\r\n\r\nThe Cisco Support and Downloads [\"https://www.cisco.com/c/en/us/support/index.html\"] page on Cisco.com provides information about licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool. Please note that customers may download only software that was procured from Cisco directly or through a Cisco authorized reseller or partner and for which the license is still valid.\r\n\r\nCustomers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco Technical Assistance Center (TAC) [\"https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html\"]. Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.\r\n\r\nWhen considering software upgrades [\"https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes\"], customers are advised to regularly consult the advisories [\"https://www.cisco.com/go/psirt\"] for the relevant Cisco products to determine exposure and a complete upgrade solution. In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) [\"https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html\"] or their contracted maintenance providers.\r\n    LEGAL DISCLAIMER DETAILS\r\n\r\nCISCO DOES NOT MAKE ANY EXPRESS OR IMPLIED GUARANTEES OR WARRANTIES OF ANY KIND, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. WITHOUT LIMITING THE GENERALITY OF THE FOREGOING, CISCO DOES NOT GUARANTEE THE ACCURACY OR COMPLETENESS OF THIS INFORMATION. THIS DOCUMENT IS PROVIDED ON AN \"AS IS\" BASIS. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.\r\n\r\nCopies or summaries of the information contained in this Security Advisory may lack important information or contain factual errors. Customers are advised to visit the Cisco Security Advisories [\"https://www.cisco.com/go/psirt\"] page for the most recent version of this Security Advisory. The Cisco Product Security Incident Response Team (PSIRT) assesses only the affected and fixed release information that is documented in this advisory. See the Cisco Security Vulnerability Policy [\"https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes\"] for more information.",
        "title": "Legal Disclaimer"
      }
    ],
    "publisher": {
      "category": "vendor",
      "contact_details": "psirt@cisco.com",
      "issuing_authority": "Cisco PSIRT",
      "name": "Cisco",
      "namespace": "https://wwww.cisco.com"
    },
    "references": [
      {
        "category": "self",
        "summary": "Cisco IOS XR Software Multi-Instance Intermediate System-to-Intermediate System Denial of Service Vulnerability",
        "url": "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-isis-dos-kDMxpSzK"
      },
      {
        "category": "external",
        "summary": "Cisco Event Response: March 2026 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication",
        "url": "https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-75772"
      },
      {
        "category": "external",
        "summary": "Cisco Security Vulnerability Policy",
        "url": "https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html"
      },
      {
        "category": "external",
        "summary": "IS-IS Authentication",
        "url": "https://www.cisco.com/c/en/us/td/docs/iosxr/ncs5500/routing/24xx/configuration/guide/b-routing-cg-ncs5500-24xx/implementing-isis.html#con_1276647"
      },
      {
        "category": "external",
        "summary": "Understand Cisco IOS XR Software Maintenance Updates (SMUs)",
        "url": "https://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-xr-software/116332-maintain-ios-xr-smu-00.html#toc-hId-972485609"
      },
      {
        "category": "external",
        "summary": "Security Vulnerability Policy",
        "url": "http://www.cisco.com/web/about/security/psirt/security_vulnerability_policy.html"
      },
      {
        "category": "external",
        "summary": "Cisco Support and Downloads",
        "url": "https://www.cisco.com/c/en/us/support/index.html"
      },
      {
        "category": "external",
        "summary": "Cisco Technical Assistance Center (TAC)",
        "url": "https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html"
      },
      {
        "category": "external",
        "summary": "considering software upgrades",
        "url": "https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes"
      },
      {
        "category": "external",
        "summary": "the advisories",
        "url": "https://www.cisco.com/go/psirt"
      }
    ],
    "title": "Cisco IOS XR Software Multi-Instance Intermediate System-to-Intermediate System Denial of Service Vulnerability",
    "tracking": {
      "current_release_date": "2026-03-11T16:00:00+00:00",
      "generator": {
        "date": "2026-03-11T15:51:12+00:00",
        "engine": {
          "name": "TVCE"
        }
      },
      "id": "cisco-sa-isis-dos-kDMxpSzK",
      "initial_release_date": "2026-03-11T16:00:00+00:00",
      "revision_history": [
        {
          "date": "2026-03-11T15:51:07+00:00",
          "number": "1.0.0",
          "summary": "Initial public release."
        }
      ],
      "status": "final",
      "version": "1.0.0"
    }
  },
  "product_tree": {
    "branches": [
      {
        "branches": [
          {
            "category": "product_family",
            "name": "Cisco IOS XR Software",
            "product": {
              "name": "Cisco IOS XR Software ",
              "product_id": "CSAFPID-5834"
            }
          }
        ],
        "category": "vendor",
        "name": "Cisco"
      }
    ]
  },
  "vulnerabilities": [
    {
      "cve": "CVE-2026-20074",
      "ids": [
        {
          "system_name": "Cisco Bug ID",
          "text": "CSCwq71827"
        }
      ],
      "notes": [
        {
          "category": "other",
          "text": "Complete.",
          "title": "Affected Product Comprehensiveness"
        }
      ],
      "product_status": {
        "known_affected": [
          "CSAFPID-5834"
        ]
      },
      "release_date": "2026-03-11T16:00:00+00:00",
      "remediations": [
        {
          "category": "vendor_fix",
          "details": "Cisco has released software updates that address this vulnerability.",
          "product_ids": [
            "CSAFPID-5834"
          ],
          "url": "https://software.cisco.com"
        }
      ],
      "scores": [
        {
          "cvss_v3": {
            "baseScore": 7.4,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H",
            "version": "3.1"
          },
          "products": [
            "CSAFPID-5834"
          ]
        }
      ],
      "title": "Cisco IOS XR Software Multi-Instance Intermediate System-to-Intermediate System Denial of Service Vulnerability"
    }
  ]
}