CVE-2026-20293: 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.
Affected Software
Event History
Frequently Asked Questions
Can a user with the standard user role exploit this issue, or is administrator access required?
Administrator access is not required. An authenticated attacker with valid credentials for an account assigned either the user or admin role could exploit the vulnerability.
Is physical access alone enough to attempt exploitation?
Yes. An unauthenticated attacker with physical access to an affected device could attempt to bypass Secure Boot validation checks without needing account credentials.
Does enabling UEFI Secure Boot prevent exploitation?
No. The issue is caused by UEFI Shell memory write commands being available while UEFI Secure Boot is enabled, allowing an attacker to alter UEFI memory variables during boot.
What access path does an attacker use to carry out the bypass?
The attacker selects the UEFI Shell boot option at boot time and uses available shell commands to modify UEFI memory variables. This can enable manipulation of the preboot environment and execution of unauthorized software.