{
  "document": {
    "acknowledgments": [
      {
        "summary": "This vulnerability was found during the resolution of a Cisco TAC support case."
      }
    ],
    "category": "csaf_security_advisory",
    "csaf_version": "2.0",
    "notes": [
      {
        "category": "summary",
        "text": "A vulnerability in the Protection Against Distributed Denial of Service Attacks feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to conduct denial of service (DoS) attacks to or through the affected device.\r\n\r\nThis vulnerability is due to incorrect programming of the half-opened connections limit, TCP SYN flood limit, or TCP SYN cookie features when the features are configured in vulnerable releases of Cisco IOS XE Software. An attacker could exploit this vulnerability by attempting to flood traffic to or through the affected device. A successful exploit could allow the attacker to initiate a DoS attack to or through an affected device.\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 September 2021 release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2021 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication. [\"https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-74581\"]",
        "title": "Summary"
      },
      {
        "category": "general",
        "text": "At the time of publication, this vulnerability affected Cisco IOS XE Software releases 17.3.1 and later (but earlier than the first fixed release) if the software was in autonomous or controller mode and had one of the following enabled:\r\n\r\nHalf-opened connections limit\r\nTCP SYN flood limit\r\nTCP SYN cookie feature\r\n\r\nFor more information about which Cisco software releases are vulnerable, see the Fixed Software [\"#fs\"] section of this advisory.\r\n  Determine the Device Configuration\r\nThe half-opened connections limit, TCP SYN flood limit, or TCP SYN cookie features are enabled if any of the following configuration commands are present in the device configuration:\r\n\r\nmax-incomplete\r\nmax-incomplete tcp\r\nmax-incomplete udp\r\nmax-incomplete icmp\r\nmax-incomplete high\r\nmax-incomplete low\r\ntcp max-incomplete host\r\ntcp syn-flood limit\r\ntcp syn-flood rate per-destination\r\n\r\nTo confirm whether the data plane has been successfully programmed, use the show platform hardware qfp active feature firewall runtime command. If the configuration is defined with half-opened session limits, SYN flood limits, or SYN cookie features, the respective flag for that feature should be present: half-open, syn-flood, or syn-cookie. If one of these features is configured but the corresponding flag is not present, the device is not programmed correctly. The following example shows the flag appearance when the data plane is programmed correctly:\r\n\r\n\r\nRouter# show platform hardware qfp active feature firewall runtime\r\n.\r\n.\r\n.\r\nglobal3 0x00000081:\r\n  syn-flood                              (0x00000040)\r\n  syn-cookie                             (0x00000020)\r\n  half-open                              (0x00000080)\r\n.\r\n.\r\n.\r\nRouter#",
        "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 XR Software\r\nMeraki products\r\nNX-OS Software",
        "title": "Products Confirmed Not Vulnerable"
      },
      {
        "category": "general",
        "text": "There are no workarounds that address this vulnerability.",
        "title": "Workarounds"
      },
      {
        "category": "general",
        "text": "When considering software upgrades [\"https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes\"], customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories page [\"https://www.cisco.com/go/psirt\"], to determine exposure and a complete upgrade solution.\r\n\r\nIn 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) or their contracted maintenance providers.\r\n        Cisco IOS and IOS XE Software\r\nTo help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides the Cisco Software Checker [\"https://sec.cloudapps.cisco.com/security/center/softwarechecker.x\"] to identify any Cisco Security Advisories that impact a specific software release and the earliest release that fixes the vulnerabilities described in each advisory (\u201cFirst Fixed\u201d). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities described in all the advisories identified (\u201cCombined First Fixed\u201d).\r\n\r\nCustomers can use the Cisco Software Checker [\"https://sec.cloudapps.cisco.com/security/center/softwarechecker.x\"] to search advisories in the following ways:\r\n\r\nChoose the software and one or more releases\r\nUpload a .txt file that includes a list of specific releases\r\nEnter the output of the show version command\r\n\r\nAfter initiating a search, customers can customize the search to include all Cisco Security Advisories, a specific advisory, or all advisories in the most recent bundled publication.\r\n\r\nCustomers can also use the following form to determine whether a release is affected by any Cisco Security Advisory by entering a Cisco IOS or IOS XE Software release\u2014for example, 15.1(4)M2 or 3.13.8S:\r\n\r\n\r\n\r\nBy default, the Cisco Software Checker [\"https://sec.cloudapps.cisco.com/security/center/softwarechecker.x\"] includes results only for vulnerabilities that have a Critical or High Security Impact Rating (SIR). To include results for Medium SIR vulnerabilities, customers can use the Cisco Software Checker on Cisco.com and check the Medium check box in the drop-down list under Impact Rating when customizing a search.",
        "title": "Fixed Software"
      },
      {
        "category": "general",
        "text": "To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy [\"https://sec.cloudapps.cisco.com/security/center/resources/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 Product Security Incident Response Team (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 the resolution of a Cisco TAC support case.",
        "title": "Source"
      },
      {
        "category": "legal_disclaimer",
        "text": "THIS DOCUMENT IS PROVIDED ON AN \"AS IS\" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. 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\nA standalone copy or paraphrase of the text of this document that omits the distribution URL is an uncontrolled copy and may lack important information or contain factual errors. The information in this document is intended for end users of Cisco products.",
        "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 XE Software Protection Against Distributed Denial of Service Attacks Feature Vulnerability",
        "url": "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-tguGuYq"
      },
      {
        "category": "external",
        "summary": "Cisco Event Response: September 2021 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication",
        "url": "https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-74581"
      },
      {
        "category": "external",
        "summary": "Cisco Security Vulnerability Policy",
        "url": "https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html"
      },
      {
        "category": "external",
        "summary": "considering software upgrades",
        "url": "https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes"
      },
      {
        "category": "external",
        "summary": "Cisco\u0026nbsp;Security Advisories page",
        "url": "https://www.cisco.com/go/psirt"
      },
      {
        "category": "external",
        "summary": "Cisco\u0026nbsp;Software Checker",
        "url": "https://sec.cloudapps.cisco.com/security/center/softwarechecker.x"
      }
    ],
    "title": "Cisco IOS XE Software Protection Against Distributed Denial of Service Attacks Feature Vulnerability",
    "tracking": {
      "current_release_date": "2021-09-22T16:00:00+00:00",
      "generator": {
        "date": "2024-05-10T23:09:23+00:00",
        "engine": {
          "name": "TVCE"
        }
      },
      "id": "cisco-sa-zbfw-tguGuYq",
      "initial_release_date": "2021-09-22T16:00:00+00:00",
      "revision_history": [
        {
          "date": "2021-09-22T15:48:17+00:00",
          "number": "1.0.0",
          "summary": "Initial public release."
        }
      ],
      "status": "final",
      "version": "1.0.0"
    }
  },
  "product_tree": {
    "branches": [
      {
        "branches": [
          {
            "branches": [
              {
                "branches": [
                  {
                    "category": "service_pack",
                    "name": "17.2.1",
                    "product": {
                      "name": "17.2.1",
                      "product_id": "CSAFPID-251225"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.2.1r",
                    "product": {
                      "name": "17.2.1r",
                      "product_id": "CSAFPID-277194"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.2.1a",
                    "product": {
                      "name": "17.2.1a",
                      "product_id": "CSAFPID-277343"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.2.1v",
                    "product": {
                      "name": "17.2.1v",
                      "product_id": "CSAFPID-278002"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.2.2",
                    "product": {
                      "name": "17.2.2",
                      "product_id": "CSAFPID-278504"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.2.3",
                    "product": {
                      "name": "17.2.3",
                      "product_id": "CSAFPID-280939"
                    }
                  }
                ],
                "category": "product_version",
                "name": "17.2"
              },
              {
                "branches": [
                  {
                    "category": "service_pack",
                    "name": "17.3.1",
                    "product": {
                      "name": "17.3.1",
                      "product_id": "CSAFPID-254712"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.3.2",
                    "product": {
                      "name": "17.3.2",
                      "product_id": "CSAFPID-277099"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.3.1a",
                    "product": {
                      "name": "17.3.1a",
                      "product_id": "CSAFPID-279338"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.3.1w",
                    "product": {
                      "name": "17.3.1w",
                      "product_id": "CSAFPID-279339"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.3.2a",
                    "product": {
                      "name": "17.3.2a",
                      "product_id": "CSAFPID-280555"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.3.1x",
                    "product": {
                      "name": "17.3.1x",
                      "product_id": "CSAFPID-280783"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.3.1z",
                    "product": {
                      "name": "17.3.1z",
                      "product_id": "CSAFPID-281331"
                    }
                  }
                ],
                "category": "product_version",
                "name": "17.3"
              },
              {
                "branches": [
                  {
                    "category": "service_pack",
                    "name": "17.4.1",
                    "product": {
                      "name": "17.4.1",
                      "product_id": "CSAFPID-262588"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.4.1a",
                    "product": {
                      "name": "17.4.1a",
                      "product_id": "CSAFPID-280770"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.4.1b",
                    "product": {
                      "name": "17.4.1b",
                      "product_id": "CSAFPID-280899"
                    }
                  },
                  {
                    "category": "service_pack",
                    "name": "17.4.1c",
                    "product": {
                      "name": "17.4.1c",
                      "product_id": "CSAFPID-282116"
                    }
                  }
                ],
                "category": "product_version",
                "name": "17.4"
              }
            ],
            "category": "product_family",
            "name": "Cisco IOS XE Software"
          },
          {
            "category": "product_family",
            "name": "Cisco IOS XE Catalyst SD-WAN",
            "product": {
              "name": "Cisco IOS XE Catalyst SD-WAN ",
              "product_id": "CSAFPID-275036"
            }
          }
        ],
        "category": "vendor",
        "name": "Cisco"
      }
    ]
  },
  "vulnerabilities": [
    {
      "cve": "CVE-2021-34697",
      "ids": [
        {
          "system_name": "Cisco Bug ID",
          "text": "CSCvx15607"
        }
      ],
      "notes": [
        {
          "category": "other",
          "text": "Complete.",
          "title": "Affected Product Comprehensiveness"
        }
      ],
      "product_status": {
        "known_affected": [
          "CSAFPID-251225",
          "CSAFPID-254712",
          "CSAFPID-262588",
          "CSAFPID-277099",
          "CSAFPID-277194",
          "CSAFPID-277343",
          "CSAFPID-278002",
          "CSAFPID-278504",
          "CSAFPID-279338",
          "CSAFPID-279339",
          "CSAFPID-280555",
          "CSAFPID-280770",
          "CSAFPID-280783",
          "CSAFPID-280899",
          "CSAFPID-280939",
          "CSAFPID-281331",
          "CSAFPID-282116",
          "CSAFPID-275036"
        ]
      },
      "release_date": "2021-09-22T16:00:00+00:00",
      "remediations": [
        {
          "category": "vendor_fix",
          "details": "Cisco has released software updates that address this vulnerability.",
          "product_ids": [
            "CSAFPID-251225",
            "CSAFPID-254712",
            "CSAFPID-262588",
            "CSAFPID-277099",
            "CSAFPID-277194",
            "CSAFPID-277343",
            "CSAFPID-278002",
            "CSAFPID-278504",
            "CSAFPID-279338",
            "CSAFPID-279339",
            "CSAFPID-280555",
            "CSAFPID-280770",
            "CSAFPID-280783",
            "CSAFPID-280899",
            "CSAFPID-280939",
            "CSAFPID-281331",
            "CSAFPID-282116",
            "CSAFPID-275036"
          ],
          "url": "https://software.cisco.com"
        }
      ],
      "scores": [
        {
          "cvss_v3": {
            "baseScore": 5.8,
            "baseSeverity": "MEDIUM",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L",
            "version": "3.1"
          },
          "products": [
            "CSAFPID-251225",
            "CSAFPID-254712",
            "CSAFPID-262588",
            "CSAFPID-277099",
            "CSAFPID-277194",
            "CSAFPID-277343",
            "CSAFPID-278002",
            "CSAFPID-278504",
            "CSAFPID-279338",
            "CSAFPID-279339",
            "CSAFPID-280555",
            "CSAFPID-280770",
            "CSAFPID-280783",
            "CSAFPID-280899",
            "CSAFPID-280939",
            "CSAFPID-281331",
            "CSAFPID-282116",
            "CSAFPID-275036"
          ]
        }
      ],
      "title": "Cisco IOS XE Software Protection Against Distributed Denial of Service Attacks feature Vulnerability"
    }
  ]
}