Security Experts:

Microsoft Patches Zero-Day Vulnerability in Office

Microsoft’s January 2018 Patch Tuesday updates address more than 50 vulnerabilities, including a zero-day vulnerability in Office related to an Equation Editor flaw that has been exploited by several threat groups in the past few months.

The zero-day vulnerability, tracked as CVE-2018-0802, has been described by Microsoft as a memory corruption issue that can be exploited for remote code execution by getting targeted users to open a specially crafted file via Office or WordPad.

Microsoft has credited several researchers from Chinese companies Tencent and Qihoo 360, ACROS Security’s 0Patch Team, and experts from Check Point Software Technologies for finding the flaw.

The security hole is related to CVE-2017-11882, a 17-year-old vulnerability in the Equation Editor (EQNEDT32.EXE), which the vendor addressed with the November 2017 Patch Tuesday updates. Based on how the patch was developed, experts believe Microsoft may have lost the application’s source code, which forced it to somehow patch the executable file directly.

Microsoft replaced the Equation Editor component in Office 2007, but kept the old one as well for compatibility reasons. The problematic component has now been removed from Office.

0Patch researchers have been analyzing CVE-2017-11882, which has likely led them to discovering a new, related vulnerability. Check Point has published a blog post with the details of CVE-2018-0802 and showed how an exploit works, but they have not mentioned any attacks.

This suggests that the Chinese researchers may have been the ones who spotted the vulnerability being exploited in attacks. This would not be the first time experts at Qihoo 360 witnessed the exploitation of an Office zero-day. Back in October, after Microsoft released a patch, they reported seeing CVE-2017-11826 being leveraged to deliver malware.

If CVE-2018-0802 is related to CVE-2017-11882, there is a long list of threat actors who may be exploiting it. CVE-2017-11882 has been exploited by Iranian cyberspies, the Cobalt hacking group, someone who uses TelegramRAT, and likely others.

Microsoft’s Patch Tuesday updates also address a spoofing vulnerability in Office for Mac that has already been publicly disclosed. Sixteen of the flaws resolved this month have been rated critical, a majority affecting the scripting engine used by the Edge and Internet Explorer web browsers.

Microsoft has also rated critical a Word vulnerability (CVE-2018-0797) that can be exploited for remote code execution using specially crafted RTF files.

Adobe’s Patch Tuesday updates for this month patch only one information disclosure vulnerability in Flash Player.

Related: Microsoft Patches for CPU Flaws Break Windows, Apps

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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.