Microsoft released Windows 10 Insider Preview Build 17134 (Redstone 4) to insiders on the fast ring. This build does not contain any new features, but rather acts as a new build with security updates included. KB4100375 fixed the following vulnerabilities discovered in Redstone 4 before it was released:Addresses a PDF security issue in Microsoft Edge, Microsoft scripting engine, Windows kernel, Microsoft graphics component, Windows Server, Windows cryptography, and Windows datacenter networking. There is still no word as to whether the blocking bug was fixed that was preventing the release of the “Spring Creators Update””.”
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-releases-windows-10-insider-build-17134-rs4-to-include-security-updates/