A vulnerability in the firmware of the Cisco UCS C-Series Rack Servers could allow an authenticated, physical attacker to bypass Unified Extensible Firmware Interface (UEFI) Secure Boot validation checks and load a compromised software image on an affected device. The vulnerability is due to improper validation of the server firmware upgrade images. An attacker could exploit this vulnerability by installing a server firmware version that would allow the attacker to disable UEFI Secure Boot. A successful exploit could allow the attacker to bypass the signature validation checks that are done by UEFI Secure Boot technology and load a compromised software image on the affected device. A compromised software image is any software image that has not been digitally signed by Cisco. There are no workarounds that address this vulnerability. Cisco has released firmware updates that address this vulnerability. This advisory is available at the following link:https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20200219-ucs-boot-bypass
A vulnerability in the firmware of the Cisco UCS C-Series Rack Servers could allow an authenticated, physical attacker to bypass Unified Extensible Firmware Interface (UEFI) Secure Boot validation checks and load a compromised software image on an affected device.
The vulnerability is due to improper validation of the server firmware upgrade images. An attacker could exploit this vulnerability by installing a server firmware version that would allow the attacker to disable UEFI Secure Boot. A successful exploit could allow the attacker to bypass the signature validation checks that are done by UEFI Secure Boot technology and load a compromised software image on the affected device. A compromised software image is any software image that has not been digitally signed by Cisco.
There are no workarounds that address this vulnerability. Cisco has released firmware updates that address this vulnerability.
This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20200219-ucs-boot-bypass
This vulnerability affects the following Cisco products if they are running a vulnerable BIOS version and a vulnerable Cisco Integrated Management Controller (IMC) firmware release:
UEFI Secure Boot is enabled only in a small subset of Cisco UCS-based appliances. For all the other appliances, the feature is not used, so the vulnerability does not apply.
For information about which BIOS versions and firmware releases are vulnerable, see the Fixed Software section of this advisory.
Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.
UEFI Secure Boot was created to enhance security in the pre-boot environment. The core issue is ensuring that a system boots without introducing compromised code.
Ensuring that boot code is executed without modification requires the use of a digital signature that is provided by a trusted code creator and embedded in every executable code section. Using public/private key pairs, the code creator “signs” their code with a private key, which can be checked against a public key in a pre-stored signature before it is executed.
Because of the UEFI Secure Boot feature, the software images for the affected products are all signed by the Cisco development teams to ensure that they have not been tampered with.
For more details on the UEFI Secure Boot feature, see the Secure Boot in Modern Computer Security Solutions document.
There are no workarounds that address this vulnerability.
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 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 their appliances as indicated in the Remediation column of the following table:
| Cisco Hardware Platform | First Fixed BIOS Version | First Fixed Cisco IMC Firmware Release |
Remediation |
|---|---|---|---|
| FMC 1000, 2500, and 4500 | 4.0.1f.0 | 4.0.2h | Apply Hotfix CJ. |
| Secure Network Server 3500 | 4.0.2d | 4.0.2h | Apply the following patches: |
| Secure Network Server 3600 | 4.0.1i | 4.0.1g | Apply the following patches: |
| Threat Grid 5504 | 4.0.2d | 4.0.2h | Upgrade to Release 2.8. |
Cisco FMC 1000, 2500, and 4500
To determine the current BIOS version on a Cisco FMC, run the command sudo dmidecode -t bios -q from the Linux shell (expert mode). It is not possible to see the installed Cisco IMC firmware release, but the firmware will be upgraded as part of Hotfix CJ along with the BIOS firmware.
Cisco Secure Network Server
The current BIOS version and Cisco IMC releases are listed in the Admin > Firmware Management section of the web-based management interface. The Cisco IMC firmware release is listed as BMC.
Cisco Threat Grid
It is not possible to see the current BIOS version. Instead, the Cisco Threat Grid software release needs to be verified because the Cisco IMC firmware will be upgraded as part of Cisco Threat Grid software release 2.8. The current build number is listed in the Operations > Update Appliance section of the web-based management interface.
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.
This vulnerability was found by Emre Demirors of Cisco during internal security testing.
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 | Updated First Fixed Release for Secure Network Server 3600 | Fixed Releases | Final | 2020-JUN-01 |
| 1.0 | Initial public release. | - | Final | 2020-FEB-19 |
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