Google this week released information on a zero-day vulnerability in Windows being actively exploited in targeted attacks alongside a recently fixed Chrome flaw (CVE-2019-5786).
The Windows vulnerability has been described as a local privilege escalation in the win32k.sys kernel driver and it can be abused for a security sandbox escape.
“The vulnerability is a NULL pointer dereference in win32k!MNGetpItemFromIndex when NtUserMNDragOver() system call is called under specific circumstances,” Clement Lecigne of Google’s Threat Analysis Group explains.
The bug is believed to be exploitable only on Windows 7 systems, due to exploit mitigations Microsoft has added in newer versions of Windows. In fact, the observed exploitation of the flaw only targeted Windows 7 32-bit systems so far.
The security bug was reported to Microsoft last week, and Google decided to make the information public although a patch isn’t available yet.
According to Lecigne, they decided to publicly disclose the vulnerability due to the fact that it’s serious and is 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,” Lecigne notes.
To mitigate the vulnerability, users should consider upgrading to Windows 10. They are also encouraged to apply patches as soon as they become available.
The Chrome vulnerability exploited in the same attacks is CVE-2019-5786, which Google discovered last month and quickly addressed on March 1. The company revealed on March 5 that this flaw had been exploited in live attacks when the patch was released.
Google pushed the update (version 72.0.3626.121) through Chrome auto-update, but Lecigne now encourages users to check whether the update has been downloaded and applied or not.
The reason for this, Director of Chrome Security and Desktop Justin Schuh explains, is that the exploit for this browser vulnerability is different from those targeting previously observed zero-days in Chrome, which relied on Flash as the first exploit in the chain.
“This newest exploit is different, in that initial chain targeted Chrome code directly, and thus required the user to have restarted the browser after the update was downloaded. For most users the update download is automatic, but restart is usually a manual action,” Schuh reveals.