CAPEC Definitions / CAPEC-696
CAPEC-696: Load Value Injection
An adversary exploits a hardware design flaw in a CPU implementation of transient instruction execution in which a faulting or assisted load instruction transiently forwards adversary-controlled data from microarchitectural buffers. By inducing a page fault or microcode assist during victim execution, an adversary can force legitimate victim execution to operate on the adversary-controlled data which is stored in the microarchitectural buffers. The adversary can then use existing code gadgets and side channel analysis to discover victim secrets that have not yet been flushed from microarchitectural state or hijack the system control flow.
Extended Description
This attack is a mix of techniques used in traditional Meltdown and Spectre attacks. It uses microarchitectural data leakage combined with code gadget abuse. Intel has identified that this attack is not applicable in scenarios where the OS and the VMM (Virtual Memory Manager) are both trusted. Because of this, Intel SGX is a prime target for this attack because it assumes that the OS or VMM may be malicious.
Mitigations
Do not allow the forwarding of data resulting from a faulting or assisted instruction. Some current mitigations claim to zero out the forwarded data, but this mitigation still does not suffice.
Insert explicit “lfence” speculation barriers in software before potentially faulting or assisted loads. This halts transient execution until all previous instructions have been executed and ensures that the architecturally correct value is forwarded.
Relationships with other CAPECs
CAPEC-663: Exploitation of Transient Instruction Execution
Prerequisites
The adversary needs at least user execution access to a system and a maliciously crafted program/application/process with unprivileged code to misuse transient instruction set execution of the CPU.
The CPU incorrectly transiently forwards values from microarchitectural buffers after faulting or assisted loads
The adversary needs the ability to induce page faults or microcode assists on the target system.
Code gadgets exist that allow the adversary to hijack transient execution and encode secrets into the microarchitectural state.
Related Weaknesses
CWE-1342: Information Exposure through Microarchitectural State after Transient Execution
