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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2022.4823 Cisco IOS XE Software DNS NAT Protocol Application Layer Gateway Denial of Service Vulnerability 29 September 2022 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: ASR 1000 Series Catalyst 8500 Series Publisher: Cisco Systems Operating System: Cisco Resolution: Patch/Upgrade CVE Names: CVE-2022-20837 Original Bulletin: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-alg-dos-KU9Z8kFX Comment: CVSS (Max): 8.6 CVE-2022-20837 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H) CVSS Source: Cisco Systems Calculator: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H - --------------------------BEGIN INCLUDED TEXT-------------------- Cisco IOS XE Software DNS NAT Protocol Application Layer Gateway Denial of Service Vulnerability Priority: High Advisory ID: cisco-sa-alg-dos-KU9Z8kFX First Published: 2022 September 28 16:00 GMT Version 1.0: Final Workarounds: No workarounds available Cisco Bug IDs: CSCwa78096 CVE Names: CVE-2022-20837 CWEs: CWE-754 Summary o A vulnerability in the DNS application layer gateway (ALG) functionality that is used by Network Address Translation (NAT) in Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload. This vulnerability is due to a logic error that occurs when an affected device inspects certain TCP DNS packets. An attacker could exploit this vulnerability by sending crafted DNS packets through the affected device that is performing NAT for DNS packets. A successful exploit could allow the attacker to cause the device to reload, resulting in a denial of service (DoS) condition on the affected device. Note: This vulnerability can be exploited only by sending IPv4 TCP packets through an affected device. This vulnerability cannot be exploited by sending IPv6 traffic. 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-alg-dos-KU9Z8kFX This advisory is part of the September 2022 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 2022 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication. Affected Products o Vulnerable Products This vulnerability affects the following Cisco devices if they are running a vulnerable release of Cisco IOS XE Software that is configured for NAT operation and has the DNS ALG for TCP feature enabled. The DNS ALG feature is enabled as soon as NAT is configured on the device. ASR 1000 Series Embedded Services Processors models ESP 100-X and ESP 200-X Catalyst 8500 Series Edge Platforms models C8500-12X4QC and C8500-12X For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory. Determine the Device Configuration Determine Whether a Device is Configured to Perform NAT To determine whether NAT is active on a device (preferred method), administrators can log in to the device and use the show ip nat statistics command in the CLI. If NAT is active, the Outside interfaces and Inside interfaces sections of the command output will include at least one interface. The following example shows the output of the show ip nat statistics command for a device where NAT is active: Router# show ip nat statistics Total active translations: 1 (0 static, 1 dynamic; 0 extended) Outside interfaces: GigabitEthernet0/0/3 Inside interfaces: GigabitEthernet0/0/1 If the output of the show ip nat statistics command does not list any interfaces, NAT is not active on the device. Alternatively, issue the show running-config command in the CLI to assess whether NAT commands are present in the device configuration. If NAT is active on the device, the output of the show running-config command will include the ip nat inside and ip nat outside interface commands. In the case of the NAT Virtual Interface, the ip nat enable interface command will be present. Determine Whether DNS ALG for TCP is Disabled in the NAT Configuration To determine whether the DNS ALG for TCP is disabled in the NAT configuration, use the show running-config | include ip nat service dns privileged EXEC command. The presence of no ip nat service dns tcp in the output of show running-config | include ip nat service dns indicates that the DNS ALG for TCP is disabled in the NAT configuration. The following is the output of show running-config | include ip nat in Cisco IOS XE Software that has the DNS ALG disabled in the NAT configuration: Router#show running-config | include ip nat service no ip nat service dns tcp If no ip nat service dns tcp does not appear in the output of show running-config | include ip nat service dns , and the device runs an affected version of Cisco IOS XE Software with NAT enabled, that configuration is vulnerable. Products Confirmed Not Vulnerable Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability. Cisco has confirmed that this vulnerability does not affect the following Cisco products: ASR 1000 Series Embedded Services Processors models ESP 100 and ESP 200, and models earlier than these Catalyst 8500 Series Edge Platforms model C8500L-8S4X IOS Software IOS XR Software NX-OS Software Workarounds o There are no workarounds that address this vulnerability. However, a mitigation is available. Administrators may mitigate this vulnerability by disabling the NAT ALG for DNS TCP packets. However, this action may negatively impact normal operation of any device that sends or receives traffic through the affected device and, consequently, may disrupt normal network operations. Administrators should verify that their network environment does not require use of a NAT ALG for DNS packets before they disable this functionality. To disable use of the NAT ALG for DNS packets, administrators can use the no ip nat service dns tcp command in global configuration mode. While 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 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. Fixed Software o Cisco has released free software updates 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. 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. The Cisco Support and Downloads 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. When considering software upgrades , customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories 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. Cisco IOS and IOS XE Software To help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides the Cisco Software Checker . This tool identifies any Cisco security advisories that impact a specific software release and the earliest release that fixes the vulnerabilities that are described in each advisory ("First Fixed"). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities that are described in all the advisories that the Software Checker identifies ("Combined First Fixed"). To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to determine whether a release is affected by any Cisco Security Advisory. To use the form, follow these steps: 1. Choose which advisories the tool will search-only this advisory, only advisories with a Critical or High Security Impact Rating (SIR) , or all advisories. 2. Enter a release number-for example, 15.9(3)M2 or 17.3.3. 3. Click Check 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. Related to This Advisory o Cisco Event Response: September 2022 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication URL o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-alg-dos-KU9Z8kFX Revision History o +----------+---------------------------+----------+--------+--------------+ | Version | Description | Section | Status | Date | +----------+---------------------------+----------+--------+--------------+ | 1.0 | Initial public release. | - | Final | 2022-SEP-28 | +----------+---------------------------+----------+--------+--------------+ - --------------------------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. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: https://www.auscert.org.au/bulletins/ =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). 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