{ "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", "title": "Summary", "text": "A vulnerability in the bidirectional forwarding detection (BFD) hardware offload feature of Cisco IOS XR Software for Cisco ASR 9000 Series Aggregation Services Routers, ASR 9902 Compact High-Performance Routers, and ASR 9903 Compact High-Performance Routers could allow an unauthenticated, remote attacker to cause a line card to reset, resulting in a denial of service (DoS) condition.\r\n\r\nThis vulnerability is due to the incorrect handling of malformed BFD packets that are received on line cards where the BFD hardware offload feature is enabled. An attacker could exploit this vulnerability by sending a crafted IPv4 BFD packet to an affected device. A successful exploit could allow the attacker to cause line card exceptions or a hard reset, resulting in loss of traffic over that line card while the line card reloads.\r\n\r\nCisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.\r\n\r\nThis advisory is available at the following link:\r\nhttps://sec.cloudapps.cisco.com [\"https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-bfd-XmRescbT\"]/security/center/content/CiscoSecurityAdvisory/cisco-sa-bfd-XmRescbT [\"https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-bfd-XmRescbT\"]\r\n\r\nThis advisory is part of the March 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: March 2023 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication [\"https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-74917\"]." }, { "category": "general", "title": "Vulnerable Products", "text": "This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco IOS XR 64-bit Software and have BFD hardware offload enabled for any of the installed line cards:\r\n\r\nASR 9000 Series Aggregation Services Routers only if they have a Lightspeed or Lightspeed-Plus-based line card installed\r\nASR 9902 Compact High-Performance Routers\r\nASR 9903 Compact High-Performance Routers\r\n\r\nFor information about which Cisco software releases are vulnerable, see the Fixed Software [\"#fs\"] section of this advisory.\r\n Determine Which Line Cards are Installed\r\nTo determine which line cards are installed in the device, use the show platform CLI command.\r\n\r\nCisco ASR 9902 and 9903 Compact High-Performance Routers integrate a Lightspeed-Plus-based line card.\r\n\r\nThe following line cards are Lightspeed-based:\r\n\r\nA9K-16X100GE-TR\r\nA99-16X100GE-X-SE\r\nA99-32X100GE-TR\r\n\r\nThe following line cards are Lightspeed-Plus-based:\r\n\r\nA9K-4HG-FLEX-SE\r\nA9K-4HG-FLEX-TR\r\nA9K-8HG-FLEX-SE\r\nA9K-8HG-FLEX-TR\r\nA9K-20HG-FLEX-SE\r\nA9K-20HG-FLEX-TR\r\nA99-4HG-FLEX-SE\r\nA99-4HG-FLEX-TR\r\nA99-10X400GE-X-SE\r\nA99-10X400GE-X-TR\r\nA99-32X100GE-X-SE\r\nA99-32X100GE-X-TR\r\n\r\nFor more information about line card type identification, see ASR 9000 Series Line Card Types [\"https://www.cisco.com/c/en/us/support/docs/routers/asr-9000-series-aggregation-services-routers/116726-qanda-product-00.html\"].\r\n\r\nNote: The Cisco Lightspeed-Plus list of product identifiers was accurate at the time of publication. For specific questions and further clarification about a product identifier, contact the Cisco Technical Assistance Center (TAC).\r\n Determine Whether BFD Hardware Offload is Enabled\r\nTo determine which line cards have BFD hardware offload enabled, use the show bfd hw-offload state CLI command. If the configuration and operational states are enabled on one of the previously mentioned line cards, the device is affected by this vulnerability. The following example shows a device in which BFD hardware offload is not enabled:\r\n\r\n\r\nRP/0/RSP0/CPU0:ASR9006#show bfd hw-offload state\r\nWed Mar 8 16:00:00.000 UTC BFD HW OFFLOAD Feature state: 0/2/CPU0 ----------------- Configuration State: Disabled Operational State: Disabled RP/0/RSP0/CPU0:ASR9006#\r\n\r\nThe following example shows a device in which BFD hardware offload is enabled:\r\n\r\n\r\nRP/0/RSP0/CPU0:ASR9006#show bfd hw-offload state\r\nWed Mar 8 16:00:00.000 UTC BFD HW OFFLOAD Feature state: 0/2/CPU0 ----------------- Configuration State: Enabled Operational State: Enabled RP/0/RSP0/CPU0:ASR9006#\r\n\r\nNot all BFD sessions are handled in hardware even if BFD hardware offload is enabled. At least one BFD session has to indicate H/W as Yes, as shown in the following example:\r\n\r\n\r\nRP/0/RSP0/CPU0:ASR9006#show bfd all session\r\nWed Mar 8 16:00:00.000 UTC IPv4: ----- Interface Dest Addr Local det time(int*mult) State\r\nEcho Async H/W NPU ---------- ------------- ------------ ---------------- ---------- ti100 10.0.0.1 0s(0s*0) 900ms(300ms*3) UP\r\nNo n/a\r\nHu0/2/0/15 192.168.100.100 0s(0s*0) 900ms(300ms*3) UP\r\nYes 0/2/CPU0 RP/0/RSP0/CPU0:ASR9006#" }, { "category": "general", "title": "Products Confirmed Not Vulnerable", "text": "Only products listed in the Vulnerable Products [\"https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-lsplus-Z6AQEOjk#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\nIOS XR Platforms not listed in the Vulnerable Products [\"https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-lsplus-Z6AQEOjk#vp\"] section of this advisory\r\nNX-OS Software" }, { "category": "general", "title": "Details", "text": "This vulnerability cannot be exploited with IPv6 BFD packets. However, if an IPv6 BFD session also has an IPv4 address configured on the attached interface, an attacker could exploit this vulnerability by sending a crafted IPv4 BFD packet to the configured IPv4 address on the interface. If interface Te0/1/0/10/0 was also configured with IPv4 address 192.168.1.1, the attacker could exploit the IPv6 BFD session by sending a crafted IPv4 BFD packet to 192.168.1.1, as shown in the following example:\r\n\r\n\r\nRP/0/RSP0/CPU0:ASR9006#show bfd all session\r\nWed Mar 8 16:00:00.000 UT IPv4: ----- IPv6: ----- Interface Dest Addr Local det time(int*mult) State H/W NPU Echo Async ------------------- --------------- ---------------- ---------------- ---------- Te0/1/0/10/0 fe80::36f8:e7ff:fee0:947 Yes 0/1/CPU0 0s(0s*0) 900ms(300ms*3) UP" }, { "category": "general", "title": "Workarounds", "text": "There is a workaround and a mitigation that address this vulnerability.\r\n\r\nThe only workaround that fully mitigates this vulnerability is disabling BFD hardware offload. Creating Infrastructure Access Control Lists (iACLs) is a mitigation that only limits the attack surface.\r\n\r\nDisable BFD Hardware Offload\r\n\r\nTo disable BFD hardware offload, remove any of the hw-module bfw-hw-offload enable commands and reset the assigned line card, as shown in the following example:\r\n\r\n\r\nRP/0/RSP0/CPU0:ASR9006#config terminal\r\nWed Mar 8 16:00:00.000 UTC\r\nRP/0/RSP0/CPU0:ASR9006(config)#no hw-module bfd-hw-offload enable location 0/2/CPU0\r\nRP/0/RSP0/CPU0:ASR9006(config)#commit\r\nRP/0/RSP0/CPU0:ASR9006(config)#end\r\nRP/0/RSP0/CPU0:ASR9006#hw-module subslot 0/2/CPU0 reload\r\n\r\n\r\nCreate Infrastructure Access Control Lists\r\n\r\nWhile iACLs limit the attack surface, they do not prevent exploitation from allowed peers and are subject to spoofing.\r\n\r\nThe following example shows an iACL that allows only infrastructure BFD peers (where 192.0.2.x/24 is the infrastructure address space):\r\n\r\n\r\nRP/0/RSP0/CPU0:ASR9006# show running-config ipv4 access-list\r\nipv4 access-list BFD_DROP\r\n5 remark * Mark sure to Allow Legitimate BFD peers *\r\n 10 permit udp 192.0.2.0 0.0.0.255 192.0.2.0 0.0.0.255 eq bfd\r\n11 remark * Depending on BFD deployment may need *\r\n12 permit udp 192.0.2.0 0.0.0.255 192.0.2.0 0.0.0.255 eq 4784\r\n 13 permit udp 192.0.2.0 0.0.0.255 192.0.2.0 0.0.0.255 eq 6784\r\n15 remark * Drop all other attempts to the infrastructure address space *\r\n 20 deny udp any 192.0.2.0 0.0.0.255 eq bfd\r\n 30 permit ipv4 any any\r\n!\r\nRP/0/RSP0/CPU0:ASR9006#\r\n\r\nApply this iACL to all exposed interfaces.\r\n\r\nThe following example shows an iACL that allows only BFD packets with a Time to Live (TTL) of 255 (expected for single hop sessions):\r\n\r\n\r\nRP/0/RSP0/CPU0:ASR9006# show running-config ipv4 access-list\r\nipv4 access-list BFD_DROP_TTL\r\n5 remark * Drop based purely on TTL. Allow our Single Hop BFD sessions *\r\n10 permit udp any 192.0.2.0 0.0.0.255 eq bfd ttl eq 255\r\n11 remark * Depending on BFD deployment may need *\r\n12 permit udp any 192.0.2.0 0.0.0.255 eq 4784 ttl eq 255\r\n13 permit udp any 192.0.2.0 0.0.0.255 eq 6784 ttl eq 255\r\n14 remark * You would need to tune the above two lines for multi-hop sessions *\r\n15 remark * Deny anything else for BFD *\r\n20 deny udp any any eq bfd ttl lt 255\r\n21 remark * You would need to tune the above line for multi-hop sessions *\r\n30 permit ipv4 any any\r\n!\r\nRP/0/RSP0/CPU0:ASR9006#\r\n\r\nApply this iACL to all exposed interfaces.\r\n\r\nWhile this workaround and mitigation have been deployed and were 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." }, { "category": "general", "title": "Fixed Software", "text": "Cisco has released free software updates [\"https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#ssu\"] that address the vulnerability described in this advisory. Customers with service contracts that entitle them to regular software updates should obtain security fixes through their usual update channels.\r\n\r\nCustomers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license:\r\nhttps://www.cisco.com/c/en/us/products/end-user-license-agreement.html [\"https://www.cisco.com/c/en/us/products/end-user-license-agreement.html\"]\r\n\r\nAdditionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.\r\n\r\nThe Cisco Support and Downloads page [\"https://www.cisco.com/c/en/us/support/index.html\"] 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.\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 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 Customers Without Service Contracts\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 TAC: https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html [\"https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html\"]\r\n\r\nCustomers 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 Fixed Releases\r\nIn the following table, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerability that is described in this advisory and the first release that includes the fix for this vulnerability. Customers are advised to upgrade to an appropriate fixed software release [\"https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes\"] as indicated in this section.\r\n Cisco IOS XR Software Release First Fixed Release 6.5 Migrate to a fixed release. 6.6 Migrate to a fixed release. 7.0 Migrate to a fixed release. 7.1 Migrate to a fixed release. 7.3 Migrate to a fixed release. 7.4 Migrate to a fixed release. 7.5 7.5.3 7.6 7.6.2 7.7 and later 7.7.1\r\nCisco has released the following SMUs to address this vulnerability.\r\n\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 Cisco IOS XR Software Release Platform SMU Name 7.1.3 ASR9K-X64 asr9k-x64-7.1.3.CSCwc39336 7.3.2 ASR9K-X64 asr9k-x64-7.3.2.CSCwc39336 7.5.2 ASR9K-X64 asr9k-x64-7.5.2.CSCwc39336\r\nThe Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory." }, { "category": "general", "title": "Vulnerability Policy", "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." }, { "category": "general", "title": "Exploitation and Public Announcements", "text": "The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory." }, { "category": "general", "title": "Source", "text": "This vulnerability was found during the resolution of a Cisco TAC support case." }, { "category": "legal_disclaimer", "title": "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." } ], "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 for ASR 9000 Series Routers Bidirectional Forwarding Detection Denial of Service Vulnerability", "url": "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-bfd-XmRescbT" }, { "category": "external", "summary": "Cisco Event Response: March 2023 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication", "url": "https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-74917" }, { "category": "external", "summary": "Cisco Security Vulnerability Policy", "url": "https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html" }, { "category": "external", "summary": "ASR 9000 Series Line Card Types", "url": "https://www.cisco.com/c/en/us/support/docs/routers/asr-9000-series-aggregation-services-routers/116726-qanda-product-00.html" }, { "category": "external", "summary": "Vulnerable Products", "url": "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-lsplus-Z6AQEOjk#vp" }, { "category": "external", "summary": "free software updates", "url": "https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#ssu" }, { "category": "external", "summary": "https://www.cisco.com/c/en/us/products/end-user-license-agreement.html", "url": "https://www.cisco.com/c/en/us/products/end-user-license-agreement.html" }, { "category": "external", "summary": "Cisco Support and Downloads page", "url": "https://www.cisco.com/c/en/us/support/index.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": "https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html", "url": "https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html" }, { "category": "external", "summary": "Security Vulnerability Policy", "url": "http://www.cisco.com/web/about/security/psirt/security_vulnerability_policy.html" } ], "title": "Cisco IOS XR Software for ASR 9000 Series Routers Bidirectional Forwarding Detection Denial of Service Vulnerability", "tracking": { "current_release_date": "2023-03-08T16:00:00+00:00", "generator": { "date": "2024-05-10T23:22:28+00:00", "engine": { "name": "TVCE" } }, "id": "cisco-sa-bfd-XmRescbT", "initial_release_date": "2023-03-08T16:00:00+00:00", "revision_history": [ { "date": "2023-03-08T15:32:01+00:00", "number": "1.0.0", "summary": "Initial public release." } ], "status": "final", "version": "1.0.0" } }, "product_tree": { "branches": [ { "name": "Cisco", "category": "vendor", "branches": [ { "name": "Cisco IOS XR Software", "category": "product_family", "product": { "name": "Cisco IOS XR Software ", "product_id": "CSAFPID-5834" } } ] } ] }, "vulnerabilities": [ { "cve": "CVE-2023-20049", "ids": [ { "system_name": "Cisco Bug ID", "text": "CSCwc39336" } ], "notes": [ { "category": "other", "title": "Affected Product Comprehensiveness", "text": "Complete." } ], "product_status": { "known_affected": [ "CSAFPID-5834" ] }, "release_date": "2023-03-08T16:00:00+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": 8.6, "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:N/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 for ASR 9000 Series Routers BFD Denial of Service Vulnerability" } ] }