{
  "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 access control list (ACL) processing on MPLS interfaces in the ingress direction of Cisco IOS XR Software could allow an unauthenticated, remote attacker to bypass a configured ACL.\r\n\r\nThis vulnerability is due to incomplete support for this feature. An attacker could exploit this vulnerability by attempting to send traffic through an affected device. A successful exploit could allow the attacker to bypass an ACL on the affected device.\r\n\r\nCisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.\r\n\r\n\r\n\r\nThis advisory is part of the September 2023 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: September 2023 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication [\"https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-75241\"].",
        "title": "Summary"
      },
      {
        "category": "general",
        "text": "At the time of publication, this vulnerability affected the following Cisco products if they were running a vulnerable release of Cisco IOS XR Software and had MPLS packet filtering enabled with the explicit-null or de-aggregation label on the ingress direction:\r\n\r\nIOS XR White box (IOSXRWBD)\r\nNetwork Convergence Series (NCS) 540 Series Routers\r\nNCS 560 Series Routers\r\nNCS 5500 Series\r\nNCS 5700 Series\r\n\r\nFor information about which Cisco software releases were vulnerable at the time of publication, see the Fixed Software [\"#fs\"] section of this advisory. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.\r\n\r\nDetermine Whether Filtering of MPLS Packets on the Ingress Direction is Enabled\r\n\r\nTo determine whether filtering of MPLS packets on the ingress direction is enabled, follow this two-step process:\r\n\r\nIdentify all MPLS interfaces.\r\nCheck the configuration to see if an IPv4 or IPv6 ACL is configured for the ingress direction.\r\n\r\nThe following example shows an MPLS interface TenGigE0/0/0/0 that has both an IPv4 and an IPv6 ACL configured on the ingress direction. In the show mpls interfaces, if the Enabled column has a Yes present, then MPLS is enabled on that interlace:\r\n\r\n\r\nRP/0/RP0/CPU0:NCS5501-1##show mpls interfaces\r\nThu Mar 16 02:47:56.142 UTC\r\nInterface                  LDP      Tunnel   Static   Enabled\r\n-------------------------- -------- -------- -------- --------\r\nTenGigE0/0/0/0             No       No       No       Yes\r\nTenGigE0/0/0/1             No       No       No       Yes\r\nRP/0/RP0/CPU0:NCS5501-1#\r\n\r\n\r\nThe device is affected by this vulnerability if any of the interfaces in the preceding example have either an IPv4 or IPv6 ingress ACL applied, as shown in the following example:\r\n\r\n\r\nRP/0/RP0/CPU0:NCS5501-1#show run interface TenGigE0/0/0/0\r\n!\r\ninterface TenGigE0/0/0/0\r\n description ** Example where IPv4 and IPv6 ACL ingress applied **\r\n ipv4 address 192.168.12.1 255.255.255.0\r\n ipv4 access-group CVE-2023-20191 ingress\r\nipv6 access-group CVE-2023-20191 ingress\r\n!\r\nRP/0/RP0/CPU0:NCS5501-1#\r\n\r\nIP ingress ACL filtering on MPLS interfaces is not currently supported on any other Cisco IOS XR Platforms.",
        "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": "Exploitation of this vulnerability could allow an attacker to bypass protections that are provided by an ACL that is applied on an affected device. The overall impact of exploitation is organization-specific because it depends on the importance of the assets that the ACL was supposed to protect. Customers should evaluate how exploitation of this vulnerability would impact their network and proceed according to their own vulnerability-handling and remediation processes.\r\n\r\nThe vulnerability exists because filtering of MPLS packets with the explicit-null or de-aggregation label on the ingress direction is not supported on any Cisco IOS XR platforms. However, support was added for products listed in the Vulnerable Products [\"#vp\"] section of this advisory. When the affected device receives the labeled packet and pops the label, it then attempts to process the configured ingress ACL. If an ACL deny entry is hit, the packet is punted to generate an ICMP unreachable packet that is to be returned. Rather than dropping the packet, this path then forwards the denied packet to the destination.",
        "title": "Details"
      },
      {
        "category": "general",
        "text": "There is a workaround that addresses this vulnerability.\r\n\r\nCustomers could remove the ingress ACLs from the MPLS-enabled interfaces and use egress ACLs in their environment. Egress hybrid ACLs are supported in Cisco IOS XR releases 7.6.2 and later.\r\n\r\nWhile this workaround 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 workaround or 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 workarounds or mitigations before first evaluating the applicability to their own environment and any impact to such environment.",
        "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      Fixed Releases\r\nAt the time of publication, the release information in the following table(s) was accurate. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.\r\n\r\nThe left column lists Cisco software releases, and the right column indicates whether a release was affected by the vulnerability that is described in this advisory and which release included the fix for this vulnerability.\r\n        Cisco IOS XR Software Release  First Fixed Release          6.3 and earlier  Not Affected.      6.4 - 6.6  Migrate to a fixed release.      7.0 - 7.6  Migrate to a fixed release or apply available SMU.      7.7  7.7.21      7.8  Migrate to a fixed release.      7.9  7.9.2      7.10  7.10.1\r\nCisco has released the following SMUs to address this vulnerability:\r\n           Cisco IOS XR Software Release  Platform  SMU Name          7.0.1  NCS5500  ncs5500-7.0.1.CSCwe63504      7.2.1  IOSXRWBD  iosxrwbd-7.2.1.CSCwe63504      7.4.15  IOSXRWBD  iosxrwbd-7.4.15.CSCwe63504      7.7.2  IOSXRWBD  iosxrwbd-7.7.2.CSCwe63504      7.7.2  NCS540L  ncs540l-aarch64-7.7.2.CSCwe63504      7.7.2  NCS5500  ncs5500-7.7.2.CSCwe63504\r\nNote: Customers who require SMUs for releases that are not listed in the following table are advised to contact their support organization.\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 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 XR Software Access Control List Bypass Vulnerability",
        "url": "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-dnx-acl-PyzDkeYF"
      },
      {
        "category": "external",
        "summary": "Cisco Event Response: September 2023 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication",
        "url": "https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-75241"
      },
      {
        "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 Security Advisories page",
        "url": "https://www.cisco.com/go/psirt"
      },
      {
        "category": "external",
        "summary": "Security Vulnerability Policy",
        "url": "http://www.cisco.com/web/about/security/psirt/security_vulnerability_policy.html"
      }
    ],
    "title": "Cisco IOS XR Software Access Control List Bypass Vulnerability",
    "tracking": {
      "current_release_date": "2023-09-13T16:00:00+00:00",
      "generator": {
        "date": "2024-05-10T23:26:33+00:00",
        "engine": {
          "name": "TVCE"
        }
      },
      "id": "cisco-sa-dnx-acl-PyzDkeYF",
      "initial_release_date": "2023-09-13T16:00:00+00:00",
      "revision_history": [
        {
          "date": "2023-09-13T15:47:29+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-2023-20191",
      "ids": [
        {
          "system_name": "Cisco Bug ID",
          "text": "CSCwe63504"
        }
      ],
      "notes": [
        {
          "category": "other",
          "text": "Complete.",
          "title": "Affected Product Comprehensiveness"
        }
      ],
      "product_status": {
        "known_affected": [
          "CSAFPID-5834"
        ]
      },
      "release_date": "2023-09-13T16:00:00+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": 5.8,
            "baseSeverity": "MEDIUM",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N",
            "version": "3.1"
          },
          "products": [
            "CSAFPID-5834"
          ]
        }
      ],
      "title": "Cisco IOS XR Software Access Control List Bypass Vulnerability"
    }
  ]
}