Disclosing vulnerabilities to protect users across platforms

Posted by Clement Lecigne, Threat Analysis Group

On Wednesday, February 27th, we reported two 0-day vulnerabilities — previously publicly-unknown vulnerabilities — one affecting Google Chrome and another in Microsoft Windows that were being exploited together.

To remediate the Chrome vulnerability (CVE-2019-5786), Google released an update for all Chrome platforms on March 1; this update was pushed through Chrome auto-update. We encourage users to verify that Chrome auto-update has already updated Chrome to 72.0.3626.121 or later.

The second vulnerability was in Microsoft Windows. It is a local privilege escalation in the Windows win32k.sys kernel driver that can be used as a security sandbox escape. The vulnerability is a NULL pointer dereference in win32k!MNGetpItemFromIndex when NtUserMNDragOver() system call is called under specific circumstances.

We strongly believe this vulnerability may only be exploitable on Windows 7 due to recent exploit mitigations added in newer versions of Windows. To date, we have only observed active exploitation against Windows 7 32-bit systems.

Pursuant to Google’s vulnerability disclosure policy, when we discovered the vulnerability we reported it to Microsoft. Today, also in compliance with our policy, we are publicly disclosing its existence, because it is a serious vulnerability in Windows that we know was being actively exploited in targeted attacks. The unpatched Windows vulnerability can still be used to elevate privileges or combined with another browser vulnerability to evade security sandboxes. Microsoft have told us they are working on a fix.

As mitigation advice for this vulnerability users should consider upgrading to Windows 10 if they are still running an older version of Windows, and to apply Windows patches from Microsoft when they become available. We will update this post when they are available.