Microsoft's Resilient File System (ReFS) is a filesystem primarily found on Windows Server machines, designed for large-scale storage with built-in data integrity and resiliency. Its kernel driver parses a complex set of on-disk structures, most of which have very little official documentation, though the ReFuzz paper (2022) provided an extended foundation that proved invaluable during this research. In this talk, I will walk through the internals of ReFS, the strategies used to attack the driver, and the vulnerabilities discovered along the way. Multiple vulnerabilities were found including CVE-2026-49793 and CVE-2026-49792, which can be triggered by just mounting a crafted disk and performing some basic I/O with standard user privileges. The vulnerabilities were found in ReFS on-disk structures, particularly compression-related ones that have never been publicly documented previously.

This talk will walk through the internals of ReFS, the different strategies used to attack the driver, and the vulnerabilities discovered along the way.