Researcher Finds a Way to Bypass Meltdown Patches on Windows 10

An anonymous reader writes: Microsoft's patches for the Meltdown vulnerability have had a fatal flaw all these past months, according to Alex Ionescu, a security researcher with cyber-security firm Crowdstrike. Only patches for Windows 10 versions were affected, the researcher wrote today in a tweet. Microsoft quietly fixed the issue on Windows 10 Redstone 4 (v1803), also known as the April 2018 Update, released on Monday.

"Welp, it turns out the Meltdown patches for Windows 10 had a fatal flaw: calling NtCallEnclave returned back to user space with the full kernel page table directory, completely undermining the mitigation," Ionescu wrote. Ionescu pointed out that older versions of Windows 10 are still running with outdated and bypass-able Meltdown patches.

Microsoft issued today an security update, but it wasn't to backport the "fixed" Meltdown patches for older Windows 10 versions. Instead, the emergency update fixed a vulnerability in the Windows Host Compute Service Shim (hcsshim) library (CVE-2018-8115) that allows an attacker to remotely execute code on vulnerable systems.