This vulnerability refers to a flaw in AMD CPU ROM microcode patch loader, which is responsible for loading microcode updates into the processor. The issue is related to improper signature verification, meaning the system does not correctly verify whether the loaded microcode is legitimate and signed by AMD.
Breakdown of the Vulnerability:
- Improper Signature Verification
- When the CPU loads a microcode update, it should only accept updates signed by AMD to prevent unauthorized modifications.
- In this case, due to a flaw in the verification process, an attacker could load a malicious microcode update.
- Attacker Requires Local Admin Privileges
- The attacker needs administrator (root) access to the system to exploit this flaw.
- This means a standard user cannot exploit it directly, but a compromised admin account could.
- Loading Malicious Microcode
- Microcode is low-level software that controls CPU behavior.
- By injecting a malicious microcode update, an attacker can alter how the CPU executes instructions.
- Impact on AMD SEV-SNP (Secure Encrypted Virtualization – Secure Nested Paging)
- SEV-SNP is an AMD technology designed to protect virtual machines (VMs) from malicious hypervisors by encrypting and isolating memory.
- A compromised microcode could potentially bypass these security protections, allowing an attacker to access and manipulate confidential data inside a VM.
Consequences:
- Loss of Confidentiality → The attacker can read sensitive data from protected virtual machines.
- Loss of Integrity → The attacker can modify data inside the VM, leading to potential security breaches.
Mitigation:
- AMD will likely release microcode updates to fix the signature verification flaw.
- System administrators should apply firmware and microcode updates promptly.
- Limiting local administrator privileges and using hardware-based attestation mechanisms can reduce the risk.