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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2023.1725 Cisco IOS XE Software Virtual Fragmentation Reassembly Denial of Service Vulnerability 23 March 2023 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Cisco IOS XE Software Publisher: Cisco Systems Operating System: Cisco Resolution: Patch/Upgrade CVE Names: CVE-2023-20027 Original Bulletin: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ipv4-vfr-dos-CXxtFacb Comment: CVSS (Max): 8.6 CVE-2023-20027 (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 Virtual Fragmentation Reassembly Denial of Service Vulnerability Priority: High Advisory ID: cisco-sa-ipv4-vfr-dos-CXxtFacb First Published: 2023 March 22 16:00 GMT Version 1.0: Final Workarounds: No workarounds available Cisco Bug IDs: CSCwb45422 CVE Names: CVE-2023-20027 Summary o A vulnerability in the implementation of the IPv4 Virtual Fragmentation Reassembly (VFR) feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper reassembly of large packets that occurs when VFR is enabled on either a tunnel interface or on a physical interface that is configured with a maximum transmission unit (MTU) greater than 4,615 bytes. An attacker could exploit this vulnerability by sending fragmented packets through a VFR-enabled interface on an affected device. A successful exploit could allow the attacker to cause the device to reload, 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://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ipv4-vfr-dos-CXxtFacb This advisory is part of the March 2023 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: March 2023 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication . Affected Products o Vulnerable Products This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco IOS XE Software and have the VFR feature enabled: 1000 Series Integrated Services Routers 4000 Series Integrated Services Routers Catalyst 8000V Edge Software Routers Catalyst 8200 Series Edge Platforms Catalyst 8300 Series Edge Platforms Catalyst 8500L Series Edge Platforms Cloud Services Router 1000V Series For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory. Determine the Device Configuration To determine whether a device is configured for VFR or has a non-default MTU, use the show running-config | include interface | ip virtual-reassembly | mtu CLI command. If the VFR feature is enabled or the MTU has been changed, this command will return ip virtual-reassembly and/or mtu under the enabled interfaces, as shown in the following example: Router# show running-config | include interface | ip virtual-reassembly | mtu interface GigabitEthernet0/0/1 mtu 9000 ip virtual-reassembly interface Tunnel1 ip virtual-reassembly Router# In this example, the physical interface GigabitEthernet0/0/1 has VFR enabled and an MTU configured at greater than 4,615 bytes. This means it is affected by this vulnerability. Interface Tunnel1, which has VFR enabled with the default MTU, is also affected by this vulnerability. Note: VFR is automatically enabled by features such as Network Address Translation (NAT), Zone-Based Firewall, and IPSec to process Layer 4 or Layer 7 information. Disabling VFR is not recommended. 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: IOS Software IOS XR Software Meraki products NX-OS Software Workarounds o There are no workarounds that address this vulnerability. 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. Subscribe to Cisco Security Notifications o Subscribe Related to This Advisory o Cisco Event Response: March 2023 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication URL o https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ipv4-vfr-dos-CXxtFacb Revision History o +----------+---------------------------+----------+--------+--------------+ | Version | Description | Section | Status | Date | +----------+---------------------------+----------+--------+--------------+ | 1.0 | Initial public release. | - | Final | 2023-MAR-22 | +----------+---------------------------+----------+--------+--------------+ Legal Disclaimer o 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. A 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. - --------------------------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). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: https://auscert.org.au/gpg-key/ iQIVAwUBZBu3/8kNZI30y1K9AQhQUg//XS0Z6HPfFm9FtnyPo+TEQtpB21LZBnTP U6U5lmwlr8Lz9lWoutp38eY3zCMvBzM+01ZoLHcOSEHausxDgvQ7lSrCQPmNV/nN 6Ra37G8Pe8c74ogGCf4fsIEVmajhO8hlV/VPmxipiTqkcemPgfZ5BII3K3ZXnLsl yKBZngK7HqIvSJNAbvs4LkKOka4GFGOyPegVLosEsJGPhPn9UItreR4Gcjl4tMDn HxfxfLo5wuSdXVLtNxl5iChW5YNR8Qc0Wcsh87q4NgwG9ShPRQh0IUTfM1PQfCQ9 JQtzNI1tfjwLZtJaf0Y7f8QqRYhKGdSB7w7BQCdq7NoKJP2aIJnsWVfY2FUxeLgg vHU2CezOqFttbeGpsZ8WjvzMHAEOwWqyRN+RNWEnDxvdS45BGX454O9dSB4e4BYd dtdcgtw9vGsOlO3lUjFxx4cfAzEnF/UQ9beKc1IyIewvPHt+/j04xY2S+TiP1+7X dEnXkYsPgb1U0yrS9yJH9ldGT2cU2TNf5RZPajFM3K0iwHsSeiDe30s3Swz0PCOk dOml5v+6CkUOKwI+fErpVeUziJN8U2vnKCH+NsH6UUSFUTku3fFfzKU1kumDl1eG soAdqvJkvg1fIA8X+6HYCDJu0IjryRQXqewpXwvNf3KyhPdHFL1MNo2mIsEd/El0 +REBrUR0Z8Y= =kIH3 -----END PGP SIGNATURE-----