# before your machine even boots..

Source: https://www.youtube.com/watch?v=QlB1-sCp6o0
Recap page: https://rapidrecap.app/video/QlB1-sCp6o0
Generated: 2025-12-23T16:36:16.774+00:00

---
## Quick Overview

A critical vulnerability, dubbed a "cell-flow flaw," enables pre-boot Direct Memory Access (DMA) attacks on motherboards from Gigabyte, MSI, ASUS, and ASRock because the Pre-Boot DMA Protection feature fails to correctly initialize the IOMMU early in the boot sequence, allowing an attacker with physical access to a malicious PCIe device to read or write kernel memory before the operating system loads and security features become active.

**Key Points:**
- The vulnerability, discovered by Riot Games researchers Nick Peterson and Mohamed Al-Sharifi, affects UEFI firmware implementations on motherboards from vendors like Gigabyte, MSI, ASUS, and ASRock.
- The flaw exploits a window during early boot when the IOMMU (Input-Output Memory Management Unit), which normally prevents rogue DMA access, fails to initialize correctly, even if 'Pre-Boot DMA Protection' is enabled.
- This failure allows a malicious DMA-capable PCIe device (like a DMA card) physical access to read or modify system memory (RAM) before the OS loads, enabling sophisticated hardware cheats.
- The exploit works by sending a malicious PCI TLP (Transaction Layer Packet) with a virtual kernel address that the improperly configured IOMMU translates to a physical memory location, bypassing safeguards.
- Riot Games' kernel-level anti-cheat, Vanguard, blocks Valorant from launching on affected systems until firmware updates are applied.
- The attack is particularly effective because it occurs before security tools, permission prompts, or alerts can notify the user, as the OS has not yet fully loaded its defenses.
- The security issue has received multiple identifiers, including CVE-2025-11901 (Asus), CVE-2025-14302 (Gigabyte), CVE-2025-14303 (MSI), and CVE-2025-14304 (ASRock).

![Screenshot at 00:04: A screenshot of the Bleeping Computer article headline: "New UEFI flaw enables pre-boot attacks on motherboards from Gigabyte, MSI, ASUS, ASRock," setting the context for the hardware security vulnerability being discussed.](https://ss.rapidrecap.app/screens/QlB1-sCp6o0/00-00-04.jpg)

**Context:** The video discusses a significant security vulnerability affecting PC motherboards where flaws in the UEFI firmware implementation allow for Direct Memory Access (DMA) attacks during the early boot process. DMA is a hardware feature allowing devices like graphics cards to read/write RAM directly, bypassing the CPU. The vulnerability specifically targets the 'Pre-Boot DMA Protection' mechanism, which relies on the IOMMU (Input-Output Memory Management Unit) to enforce memory access rules for devices. The discovery was made by researchers associated with Riot Games, whose anti-cheat software, Vanguard, relies on kernel-level integrity checks, making this vulnerability a direct threat to their cheat prevention efforts.

## Detailed Analysis

The video details a critical security flaw found in the UEFI firmware of motherboards from major manufacturers (Asus, Gigabyte, MSI, ASRock) that enables pre-boot Direct Memory Access (DMA) attacks. DMA allows peripherals to read and write directly to system RAM, bypassing the CPU. Normally, the IOMMU (Input-Output Memory Management Unit) acts as a gatekeeper, checking device access requests against a memory map. However, the vulnerability arises because the 'Pre-Boot DMA Protection' feature, intended to activate the IOMMU early, often fails to initialize the IOMMU correctly during the earliest seconds of the boot process. This creates a window where a malicious PCIe device, connected physically, can send DMA transactions (PCI TLPs) targeting virtual kernel addresses. The IOMMU, being improperly configured, incorrectly translates these virtual addresses to physical memory locations, granting the malicious device unfettered read/write access to kernel memory. This allows hardware cheats to inject malicious code and hide themselves before the operating system (OS) and its security features, like Vanguard, fully load, meaning no warnings or alerts occur. The existence of this vulnerability forces Riot Games to block Valorant from launching on affected systems until firmware updates are installed. The flaw is particularly insidious because even when the protection setting is enabled in the BIOS, the underlying hardware implementation fails to set up the IOMMU mapping tables correctly until later in the boot sequence.

### DMA Attacks Explained

- DMA allows devices like GPUs to read/write RAM directly, bypassing the CPU
- This is usually restricted by the IOMMU, which acts as a memory access bouncer for RAM
- The exploit involves a malicious PCIe device sending data packets (TLPs) to a virtual kernel address

### The Vulnerability

- Pre-Boot DMA Protection settings in UEFI firmware are supposed to enable the IOMMU early, but the implementation fails to configure it correctly during the initial handoff phase of the boot sequence
- This leaves the system vulnerable to DMA writes to kernel memory before the OS loads

### Attack Mechanism

- A malicious PCIe device sends a PCI TLP with a virtual address (e.g., 0xffff0000) that the improperly configured IOMMU translates to a physical kernel address (e.g., 0xf7001234)
- This allows writing arbitrary data to kernel memory (like OS code) before security safeguards are established

### Impact and Vendors

- The vulnerability affects motherboards from AsRock, ASUS, GIGABYTE, and MSI, as confirmed by Carnegie Mellon CERT/CC
- Riot Games' Vanguard anti-cheat blocks Valorant on affected systems until firmware updates are applied

### The Solution

- Hardware manufacturers must release BIOS updates to ensure the IOMMU is properly configured and activated as early as possible in the boot sequence to prevent the IOMMU from accepting malicious translations.

![Screenshot at 00:04: Article headline detailing the UEFI flaw affecting major motherboard vendors \(Gigabyte, MSI, ASUS, ASRock\).](https://ss.rapidrecap.app/screens/QlB1-sCp6o0/00-00-04.jpg)
![Screenshot at 00:48: Diagram illustrating normal DMA flow where the CPU uses the IOMMU/MMU to translate virtual addresses \(0x7ffff123\) to physical addresses \(0x123aa035\) in RAM, and how a device interacts with the IOMMU.](https://ss.rapidrecap.app/screens/QlB1-sCp6o0/00-00-48.jpg)
![Screenshot at 01:37: Diagram showing the boot sequence layers \(UEFI, SHIM, OS\) and how the malicious write/read occurs before the OS is fully trusted.](https://ss.rapidrecap.app/screens/QlB1-sCp6o0/00-01-37.jpg)
![Screenshot at 02:23: Diagram showing the 'REALLY REALLY EVIL INTERFACE' device bypassing the IOMMU and writing directly to RAM, illustrating the consequence of the flaw.](https://ss.rapidrecap.app/screens/QlB1-sCp6o0/00-02-23.jpg)
![Screenshot at 08:00: Diagram detailing the malicious translation process where a PCI TLP with a source address \(0xffff0000\) is translated by the IOMMU using a Device ID \(RID\) to a physical kernel address \(0xf7001234\).](https://ss.rapidrecap.app/screens/QlB1-sCp6o0/00-08-00.jpg)