MIT's Fractal OS, a bare-metal research kernel developed at MIT CSAIL, has uncovered the first published evidence of Phantom speculation on Apple's M1 chip — a class of speculative execution attack previously observed only on AMD and Intel processors. The research also found that the M1's conditional branch predictor has no privilege isolation between user-space and kernel-space, directly contradicting earlier published findings that were likely skewed by macOS scheduler noise. While full arbitrary code execution was not demonstrated, observable instruction cache side-channel leakage was confirmed across user-to-user, user-to-kernel, and cross-ASID configurations. Apple's response has been atypical — requesting access to Fractal itself rather than issuing a CVE or advisory — leaving developers without official guidance. The findings challenge the long-held assumption that Apple Silicon is inherently safer from Spectre-class attacks due to its post-Spectre design.
