cisco-sa-ucs-uefi-sb-bypass-eb6xC5GW: Cisco UCS and UCS-Based Appliances UEFI Shell Secure Boot Bypass Vulnerability
A vulnerability in the Unified Extensible Firmware Interface (UEFI) Shell implementation of Cisco UCS Servers and UCS-based appliances could allow an authenticated attacker with valid credentials for a user account with the role of user or admin or an unauthenticated attacker with physical access to an affected device to bypass UEFI Secure Boot validation checks and execute unauthorized software.This vulnerability is due to the availability of memory write commands in the UEFI Shell while UEFI Secure Boot is enabled on a device. An attacker could exploit this vulnerability by selecting the UEFI Shell boot option at boot time and using available shell commands to modify UEFI memory variables. A successful exploit could allow the attacker to manipulate the preboot environment, overwrite UEFI Secure Boot-related memory values, and execute unauthorized software on the affected device.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-ucs-uefi-sb-bypass-eb6xC5GW
Affected Software
Event History
Frequently Asked Questions
Who can exploit this issue?
An attacker can exploit it either with valid credentials for an account assigned the user or admin role, or without authentication if they have physical access to an affected device.
What access is required to carry out the bypass?
The attacker must be able to select the UEFI Shell boot option during boot. They then use UEFI Shell memory write commands to modify UEFI memory variables while Secure Boot is enabled.
What is the practical impact of successful exploitation?
Successful exploitation lets an attacker manipulate the preboot environment, overwrite Secure Boot-related memory values, bypass Secure Boot validation, and execute unauthorized software.
Is there a mitigation if updates cannot be installed immediately?
No. The available data states that there are no workarounds; Cisco software updates are the remediation.