MDS attacs on Intel CPUs

Attacks on the newly-disclosed “MDS” hardware vulnerabilities in Intel CPUs

The RIDL and Fallout speculative execution attacks allow attackers to leak confidential data across arbitrary security boundaries on a victim system, for instance compromising data held in the cloud or leaking your information to malicious websites. Our attacks leak data by exploiting the newly disclosed Microarchitectural Data Sampling (or MDS) side-channel vulnerabilities in Intel CPUs. Unlike existing attacks, our attacks can leak arbitrary in-flight data from CPU-internal buffers (Line Fill Buffers, Load Ports, Store Buffers), including data never stored in CPU caches. We show that existing defenses against speculative execution attacks are inadequate, and in some cases actually make things worse. Attackers can use our attacks to obtain sensitive data despite mitigations, due to vulnerabilities deep inside Intel CPUs.


RIDL (Rogue In-Flight Data Load) shows attackers can exploit MDS vulnerabilities to mount practical attacks and leak sensitive data in real-world settings. By analyzing the impact on the CPU pipeline, we developed a variety of practical exploits leaking in-flight data from different internal CPU buffers (such as Line-Fill Buffers and Load Ports), used by the CPU while loading or storing data from memory.

We show that attackers who can run unprivileged code on machines with recent Intel CPUs – whether using shared cloud computing resources, or using JavaScript on a malicious website or advertisement – can steal data from other programs running on the same machine, across any security boundary: other applications, the operating system kernel, other VMs (e.g., in the cloud), or even secure (SGX) enclaves.

We will present our paper on these attacks at the 40th IEEE Symposium on Security and Privacy, on May 20th 2019.


Fallout demonstrates that attackers can leak data from Store Buffers, which are used every time a CPU pipeline needs to store any data. Making things worse, an unprivileged attacker can then later pick which data they leak from the CPU’s Store Buffer.

We show that Fallout can be used to break Kernel Address Space Layout Randomization (KASLR), as well as to leak sensitive data written to memory by the operating system kernel.

Ironically, the recent hardware countermeasures introduced by Intel in recent Coffee Lake Refresh i9 CPUs to prevent Meltdown make them more vulnerable to Fallout, compared to older generation hardware.

PS: This server has been updated for The RIDL and Fallout speculative execution attacks.