This is a project that we've been working in collaboration with Google and AWS. We present a vulnerability that allows a malicious virtual machine to leak all physical memory of its host, including the memory of other virtual machines running on the system. L1TF Reloaded combines two long-known transient execution vulnerabilities, L1TF and (Half-)Spectre. By combining them, commonly deployed software-based mitigations against L1TF, such as L1d flushing and core scheduling, can be circumvented.

We've demonstrated our attack on real-world KVM-based cloud solutions. Both Google Cloud [1] and AWS [2] wrote a blog post in response to this attack, where they describe how they mitigate against L1TF Reloaded and how they harden their systems against unknown transient execution attacks. Google also decided to award us a bug bounty of $151,515, the highest bounty of their Cloud VRP yet.

PoC is available at https://github.com/ThijsRay/l1tf_reloaded

[1] this submission

[2] https://aws.amazon.com/blogs/security/ec2-defenses-against-l...