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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2019.3011 Cisco IOS XR Software Intermediate System-to-Intermediate System Denial of Service Vulnerability 8 August 2019 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Cisco IOS XR Publisher: Cisco Systems Operating System: Cisco Impact/Access: Denial of Service -- Remote/Unauthenticated Resolution: Patch/Upgrade CVE Names: CVE-2019-1918 Original Bulletin: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190807-iosxr-isis-dos-1918 - --------------------------BEGIN INCLUDED TEXT-------------------- Cisco Security Advisory Cisco IOS XR Software Intermediate System-to-Intermediate System Denial of Service Vulnerability High Advisory ID: cisco-sa-20190807-iosxr-isis-dos-1918 First Published: 2019 August 7 16:00 GMT Version 1.0: Final Workarounds: No workarounds available Cisco Bug IDs: CSCvp90854 CVE-2019-1918 CWE-20 CVSS Score: Base 7.4 CVSS: 3.0/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X CVE-2019-1918 CWE-20 Summary o A vulnerability in the implementation of Intermediate System-to-Intermediate System (IS-IS) routing protocol functionality in Cisco IOS XR Software could allow an unauthenticated attacker who is in the same IS-IS area to cause a denial of service (DoS) condition. The vulnerability is due to incorrect processing of IS-IS link-state protocol data units (PDUs). An attacker could exploit this vulnerability by sending specific link-state PDUs to an affected system to be processed. A successful exploit could allow the attacker to cause incorrect calculations used in the weighted remote shared risk link groups (SRLG) or in the IGP Flexible Algorithm. It could also cause tracebacks to the logs or potentially cause the receiving device to crash the IS-IS process, resulting in a DoS condition. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. This advisory is available at the following link: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190807-iosxr-isis-dos-1918 A companion advisory is available at the following link: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/ cisco-sa-20190807-iosxr-isis-dos-1910 Affected Products o Vulnerable Products This vulnerability affects Cisco devices if they are running Cisco IOS XR Software releases later than 6.5.1 and earlier than 6.6.3. Cisco has confirmed that this vulnerability affects both Cisco IOS XR 32-bit Software and Cisco IOS XR 64-bit Software. Determining Whether the Device Has a Vulnerable Configuration To determine if the device is configured for IS-IS routing, administrators can use the show running-config router isis EXEC command in the CLI. If the router is configured with IS-IS routing, it will return output. The following example shows the output of the show running-config router isis command on a device that is configured as a level 1 IS-IS router. The device is affected if it is configured as one of the following: is-type level-1, level-1-2 or level-2-only. RP/0/RSP1/CPU0:IOSXR#show running-config router isis Sun May 26 05:20:23.088 UTC router isis core is-type level-1 net 49.0001.1921.6825.5091.00 address-family ipv4 unicast ! interface TenGigE0/0/0/1 address-family ipv4 unicast ! For the device to be exploitable, it would need at least one formed IS-IS adjacency. RP/0/RSP1/CPU0:IOSXR#show isis adjacency IS-IS p Level-1 adjacencies: System Id Interface SNPA State Hold Changed NSF BFD 12a4 PO0/1/0/1 *PtoP* Up 23 00:00:06 Capable Init 12a4 TenGigE0/0/0/1 0004.2893.f2f6 Up 56 00:04:01 Capable Up Total adjacency count: 2 ! Products Confirmed Not Vulnerable Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability. Details o Cisco recommends that customers ensure the authentication of routers within the IS-IS area for adjacency establishment (Hello packets) and for link-state PDUs when implementing IS-IS. If this best practice is followed, then only an authenticated adjacency within the same IS-IS area that sends the specific IS-IS link-state PDU could exploit this vulnerability. Cisco also recommends that customers enable Non-Stop Forwarding and/or Non-Stop Routing. Workarounds o There are no workarounds that address this vulnerability. However, following Cisco best practices and ensuring that IS-IS authentication is enabled for adjacencies (Hello packets) and link-state PDUs would restrict this vulnerability to only authenticated link-state PDUs. For example: router isis core lsp-password hmac-md5 encrypted 13061E010803 interface TenGigE0/0/0/6 hello-password hmac-md5 encrypted 094F471A1A0A ! For more information on IS-IS Authentication, see the IS-IS Authentication chapter of Implementing IS-IS on Cisco IOS XR Software. Fixed Software o Cisco has released free software updates that address the vulnerability described in this advisory. Customers 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: https://www.cisco.com/c/en/us/products/end-user-license-agreement.html Additionally, 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. When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, 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) or their contracted maintenance providers. Customers Without Service Contracts Customers 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 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. Fixed Releases Cisco fixed this vulnerability in Cisco IOS XR Software Release 6.6.3. Cisco has also released the following software maintenance upgrades (SMUs) that address this vulnerability: IOS XR Release SMU ID Platform SMU Name 6.5.3 AA15778 ASR9000 asr9k-px-6.5.3.CSCvq45118^1 6.6.1 AA15881 NC56K ncs6k-6.6.1.CSCvq45118.tar^1 ^1The SMUs contain the fixes for the vulnerabilities described in cisco-sa-20190807-iosxr-isis-dos-1910 and cisco-sa-20190807-iosxr-isis-dos-1918 advisories. Customers can download the SMUs from the Software Center on Cisco.com by doing the following: 1. Click Browse All. 2. Choose IOS and NX-OS Software > IOS XR > IOS XR Software > Optical Networking or Routers. 3. Choose the appropriate product and model. 4. Access releases by using the left pane of the appropriate product page. Exploitation and Public Announcements o 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. Source o This vulnerability was found during the resolution of a Cisco TAC support case. Cisco Security Vulnerability Policy o To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco. URL o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/ cisco-sa-20190807-iosxr-isis-dos-1918 Revision History o +----------+---------------------------+----------+---------+-----------------+ | Version | Description | Section | Status | Date | +----------+---------------------------+----------+---------+-----------------+ | 1.0 | Initial public release. | -- | Final | 2019-August-07 | +----------+---------------------------+----------+---------+-----------------+ - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. 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On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBXUuuY2aOgq3Tt24GAQiPew/9FA/WwyYn6DU8j473pdjcNsMb/+e4WJgI bUp8ib+AwQi11qgd6ZcCrf6EB6mU9rHLwZD+nTukO+Cef9GumJeRQjgpbqRdEljk Zwo+t3SXQDD6crc+WLhVbLXstZGc766Lb217x+sHX8XL8ouxoii1TRicXpgZ454j 1FEOvOmKBXNHbalXktrPuiLxPOLdgS5nqhmdoZ+smM4+MUADeaFh6HvhVCGs9QJh E+9nlXdflcdXCM8iPYt8l501O5PGk+0Qf1uMhgKNGgL9FHyfDB0jrwbKYVAodvpa kTjVa81uJeDx1gu3aU/t6iOW53JyNE2/jukQcb/llJ0Re3f21QsWNCXsn6lLfITj tcOkQPf08clyULky0nMHeTnHy76hK7FJzzOeLY/VHlzL63Rw3qK3+bNbT2PNf96n uFTWAnxkTa/97Pska5HhccziqnkPWEohvkWWoSINDwnZOQbA7Rw/S1m2L1LPGzxT bnKtOPhgbHX0VZjH0gHmxfqMWkZMUdru2OxUoEAHMWWv3sYJwS0mj3Y76Z1lVlYr J368pWQTgneW9D7LnSXkPe6ZgiN2Mmse3CEfNCWW0QxfWoX13ayapD2vIwhPs2t9 /23itStT1fXom3kD1xMfTRk+RdpOD3F82X+HRiItwCQaREGhaxAzFcAdoQHSUjst pCHgH7UyJrU= =Y2qC -----END PGP SIGNATURE-----