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Google Discloses Windows Zero-Day Vulnerability

Google has disclosed a Windows zero-day vulnerability after Microsoft failed to release a patch within the 7-day deadline the search giant gives vendors when it finds a flaw that is actively exploited by malicious actors.

Google researchers discovered recently that the Windows kernel is affected by a local privilege escalation vulnerability that allows attackers to escape the sandbox.

“[The vulnerability] can be triggered via the win32k.sys system call NtSetWindowLongPtr() for the index GWLP_ID on a window handle with GWL_STYLE set to WS_CHILD. Chrome's sandbox blocks win32k.sys system calls using the Win32k lockdown mitigation on Windows 10, which prevents exploitation of this sandbox escape vulnerability,” Google said in a blog post on Monday.

Google typically gives companies 90 days to patch vulnerabilities found by its researchers, but vendors are advised to develop fixes or at least provide workarounds within 60 days if the flaw is critical. However, if a security hole is being exploited in the wild, vendors only get 7 days to take action.

On October 21, Google informed Microsoft and Adobe of Windows and Flash Player vulnerabilities that had been actively exploited. Adobe managed to patch Flash Player a few days later, but Microsoft still hasn’t released a fix or an advisory.

“We believe in coordinated vulnerability disclosure, and today’s disclosure by Google could put customers at potential risk. Windows is the only platform with a customer commitment to investigate reported security issues and proactively update impacted devices as soon as possible. We recommend customers use Windows 10 and the Microsoft Edge browser for the best protection,” a Microsoft spokesperson said in an emailed statement.

In the case of Adobe, Google discovered that malicious actors had been exploiting a use-after-free vulnerability (CVE-2016-7855) in limited, targeted attacks aimed at users running Windows 7, 8.1 and 10.

The patches released by Microsoft in October addressed a total of four vulnerabilities exploited in the wild, including weaknesses leveraged by advanced persistent threat (APT) actors in cyber espionage operations and by profit-driven cybercriminals in malvertising attacks.

This is not the first time Google has disclosed Windows vulnerabilities before Microsoft could release a patch. In late 2014 and early 2015, Google Project Zero published the details of several flaws after the 90-day deadline expired. At the time, the company made some changes to its disclosure policy after being criticized by some members of the industry.

*Updated with statement from Microsoft

Related: Zero-Day Patched by Microsoft Used for Malvertising Since 2014

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.