The error message "Fatal error: 39 (Secure Boot Failed)" is generated by the ESXi bootloader (mboot.efi). The ESXi boot process with UEFI Secure Boot enabled follows a strict chain of trust. First, the UEFI firmware verifies the signature of the ESXi bootloader. Once the bootloader is verified and executed, its primary responsibility is to verify the digital signature of the VMkernel. The "Fatal error: 39" specifically indicates that this second step has failed; the bootloader was unable to validate the kernel's signature. This failure halts the boot process to prevent a potentially compromised or corrupted kernel from loading.

B. The Trusted Platform Module chip has failed.

The Trusted Platform Module (TPM) is primarily used for remote attestation and storing cryptographic keys, not for validating component signatures during the Secure Boot process itself.

C. The administrator attempted to boot with a bootloader that is unsigned or has been tampered with.

If the bootloader were invalid, the UEFI firmware would have blocked it from executing. The error would originate from the system's UEFI firmware, not the ESXi environment.

D. A package (VIB or driver) has been tampered with.

Packages (VIBs) are verified by the VMkernel after the kernel has been successfully loaded. A VIB signature failure would occur later in the boot sequence and result in a different error.

1. VMware vSphere Documentation

"Managing ESXi Booting with UEFI Secure Boot": "When UEFI Secure Boot is enabled on an ESXi host

the bootloader is first to be verified by the UEFI firmware. After the bootloader is verified

the bootloader verifies the ESXi kernel. Finally

the kernel verifies each VIB." This official documentation confirms the boot sequence

placing the kernel verification step immediately after the bootloader is loaded

which is when the specified error occurs.

2. VMware vSphere 8 Security Guide (PDF)

Page 49

"ESXi Secure Boot": "The ESXi bootloader contains a VMware public key. The bootloader uses this key to verify the signature of the kernel... The kernel in turn verifies the signature of every VIB that is loaded." This source explicitly states that the bootloader is responsible for verifying the kernel

reinforcing that a failure at this stage is due to a kernel issue.

3. VMware Knowledge Base Article 2147606

"ESXi host fails to boot with error: Fatal error: 39 (Secure Boot Failed)": This KB article documents the specific error message. While it describes a scenario where an outdated bootloader is the root cause of the problem (as it cannot correctly process the new kernel)

the direct trigger for the "Fatal error: 39" message is the bootloader's failure to verify the kernel signature. This supports that the error is tied to the kernel verification step.