DDRop: The $159 Attack That Breaks "Unbreakable" Cloud Encryption

A recent paper has revealed a significant flaw in the security of confidential computing technologies, which were designed to protect data even from a malicious cloud provider. Confidential computing, such as Intel's TDX and AMD's SEV-SNP, aims to ensure that memory remains encrypted while actively in use, even if the cloud provider has physical access to the server. However, researchers from KU Leuven, ETH Zurich, Durham University, and Google have found a critical vulnerability in these systems.

The attack, dubbed DDRop, involves the creation of a $159 circuit board, an interposer, that sits between the CPU and DDR5 memory. This interposer can silently drop write commands, causing the earlier value to remain in memory while the processor reads it back as though the update had happened. Crucially, the encryption engine does not detect this discrepancy, allowing the attacker to manipulate page table writes without triggering any alarms.

The implications of this vulnerability are severe. The researchers demonstrated that DDRop can grant full control over protected virtual machines on Intel TDX by manipulating page table writes, enabling unauthorized memory access and even forging attestation reports. This means a VM could falsely claim to be running untampered code, potentially leading to a complete compromise of the system.

However, the attack does have some requirements. It necessitates an attacker already possessing software control of the server and having brief physical access to install the hardware interposer. Intel and AMD have acknowledged the disclosure, noting that physical-access attacks are outside their threat model. While this is a valid point, it seems contradictory when someone specifically chooses confidential computing to defend against a malicious insider with server access.

The most concerning aspect of DDRop is that it is an architectural vulnerability, not easily mitigated by a software patch. As such, the issue lies at the hardware level and cannot be resolved through a simple software update. This presents a challenge for organizations relying on confidential computing technologies to secure their data.