Cisco Security Advisory
Cisco IOS XE Software for Cisco Catalyst 9300 Series Switches Secure Boot Bypass Vulnerability
A vulnerability in Cisco IOS XE Software for Cisco Catalyst 9300 Series Switches could allow an authenticated, local attacker with level-15 privileges or an unauthenticated attacker with physical access to the device to execute persistent code at boot time and break the chain of trust.
This vulnerability is due to errors that occur when retrieving the public release key that is used for image signature verification. An attacker could exploit this vulnerability by modifying specific variables in the Serial Peripheral Interface (SPI) flash memory of an affected device. A successful exploit could allow the attacker to execute persistent code on the underlying operating system.
Note: In Cisco IOS XE Software releases 16.11.1 and later, the complexity of an attack using this vulnerability is high. However, an attacker with level-15 privileges could easily downgrade the Cisco IOS XE Software on a device to a release that would lower the attack complexity.
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:
This vulnerability affects Cisco Catalyst 9300 Series Switches if they are running Cisco IOS XE Software with a release of Cisco IOS XE ROM Monitor (ROMMON) that is earlier than Release 17.3.7r, Release 17.6.5r, or Release 17.8.1r.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Determine the Cisco IOS XE ROMMON Release
To determine the Cisco IOS XE ROMMON release that is running on the device, use the show version | include BOOTLDR command on the device CLI. The following example shows the output of the show version | include BOOTLDR command on a device that is running Cisco IOS XE ROMMON Release 17.6.1r:
switch#show version | include BOOTLDR
BOOTLDR: System Bootstrap, Version 17.6.1r[FC2], RELEASE SOFTWARE (P)
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:
- Catalyst 9200 Series Switches
- Catalyst 9400 Series and 9400X Switches
- Catalyst 9500 Series and 9500X Switches
- Catalyst 9600 Series and 9600X Switches
- IOS Software
- IOS XR Software
- Meraki products
- NX-OS Software
There are no workarounds that address this vulnerability.
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:
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.
Customers are advised to upgrade to an appropriate fixed software release as indicated in the following table(s):
Cisco IOS XE Software Release First Fixed Release 16.11 and earlier Migrate to a fixed release. 16.12 Migrate to a fixed release. 17.1 Migrate to a fixed release. 17.2 Migrate to a fixed release. 17.3 17.3.7 (includes ROMMON 17.3.7r) 17.4 Migrate to a fixed release. 17.5 Migrate to a fixed release. 17.6 17.6.5 (includes ROMMON 17.6.5r) 17.7 Migrate to a fixed release. 17.8 Not vulnerable (includes ROMMON 17.8.1r). 17.9 Not vulnerable (includes ROMMON 17.9.1r). 17.10 Not vulnerable (includes ROMMON 17.10.1r).
- ROMMON can only be updated by upgrading to a Cisco IOS XE Software release that includes the updated ROMMON release.
- Upgrade to a Cisco IOS XE Software release that includes an updated ROMMON release that has a release number that is higher than the release number of the ROMMON release currently running on the device. For example, if you are currently running Cisco IOS XE Software Release 17.3.6 with ROMMON Release 17.6.1r, you need to upgrade to Cisco IOS XE Software Release 17.6.5 (which includes ROMMON Release 17.6.5r) or later or Cisco IOS XE Software Release 17.8.1 (which includes ROMMON Release 17.8.1r) or later. Upgrading to Cisco IOS XE Software Release 17.3.7 will not install the updated ROMMON Release 17.3.7r in this scenario, as moving from ROMMON Release 17.6.1r to Release 17.3.7r would be considered a ROMMON downgrade, which is not allowed.
- For a complete fix, customers should also upgrade ROMMON in the golden SPI flash device by using the upgrade rom-monitor capsule golden switch command. This update should be done after the automatic ROMMON upgrade in the primary SPI flash device. See the ROMMON Upgrades section of the Release Notes for Cisco Catalyst 9300 Series Switches for further information on ROMMON upgrades.
- Following the upgrade to a fixed ROMMON release, including the ROMMON upgrade in the golden SPI flash device, customers could downgrade to an earlier release of Cisco IOS XE Software but retain the fix for this vulnerability.
The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.
The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
This vulnerability was found during internal security testing by X.B. of the Cisco Advanced Security Initiatives Group (ASIG).
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.
Version Description Section Status Date 1.1 Clarified upgrade requirements. Fixed Releases Final 2023-MAY-11 1.0 Initial public release. - Final 2023-MAR-22
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