Google Discloses Unpatched Windows Bug Under Active Exploitation

Google has disclosed an unpatched flaw in the Windows kernel that it says is being actively exploited to hack systems.

The company disclosed the flaw after giving Microsoft seven days to patch it.

Google said it currently expects Microsoft to issue a fix for the bug on 10 November, along with its regular monthly set of security patches.

“Currently we expect a patch for this issue to be available on November 10,” said Ben Hawkes, team lead for Google’s Project Zero security unit, on Twitter.

Two-pronged attack

Hawkes said the issue, identified as CVE-2020-17087, was being used in conjunction with a bug in Google’s own Chrome browser to carry out attacks.

The Windows kernel flaw is only accessible locally, meaning it ordinarily would not be able to be exploited via a network.

However, attackers used a previously undetected bug in Chrome, identified as CVE-2020-15999, to target systems with malicious code over the internet.

Attackers then used the Windows kernel flaw to bypass Chrome’s security protections, in what is termed a sandbox escape, Hawkes said.

The Windows kernel flaw constitutes a “locally accessible attack surface that can be exploited for privilege escalation (such as sandbox escape)”, Project Zero confirmed in its advisory.

Targeted hacking

Project Zero has the controversial practice of giving software vendors a hard deadline after which it discloses flaws to the public, whether a patch is available or not.

In the case of bugs under active exploitation, the deadline is only seven days.

Hawkes cited Google’s Threat Analysis Group as saying that the Windows kernel flaw was being used along with the Chrome bug in “targeted exploitation”.

The attacks are “not related to any US election” targets, Hawkes said, without specifying who the targets were believed to be.

The issue affects the Windows Kernel Cryptography Driver (cng.sys) and affects Windows 7 up to the most recent version of Windows 10, Project Zero said.

The researchers also published proof-of-concept code demonstrating how to exploit the bug, which is caused by a 16-bit integer truncation issue.

The Chrome flaw was patched in Chrome version 86.0.4240.111.