Attackers Target Unpatched Microsoft Word Flaw

Office 365 Threat Intelligence

The attacks make use of a previously undisclosed bug in Windows’ Object Linking and Embedding (OLE) feature to take over users’ systems

All supported versions of Microsoft Word are vulnerable to an unpatched bug that is being actively exploited to infect users’ systems, two security firms warned over the weekend.

McAfee and FireEye both released advisories warning of the attacks, which make use of an unusual technique that involves booby-trapped Word documents sent to unsuspecting victims.

Office 2016 Office 365 Groups in Outlook 2016


Malware download

When a user opens the document – specifically, an RTF file with a .doc extension – an OLE2link object embedded in the file causes Word to connect to an attacker-controlled online address and download and execute an HTML application file, researchers said.

The .hta executable bypasses memory-based mitigations put into place by Microsoft and gives attackers the ability to execute arbitrary code on the victim’s system, McAfee said.

The exploit also downloads and displays a fake Word document to the user to conceal a user prompt generated by the OLE2link object, FireEye said.

“The exploit works on all Microsoft Office versions, including the latest Office 2016 running on Windows 10,” McAfee said in an advisory, adding it has seen exploits being carried out since late January.

Patch on the way this week

While Word-based attacks are most commonly carried out using macros, this exploit is unusual in that it makes use of Windows’ Object Linking and Embedding (OLE) feature, researchers said.

McAfee said it identified the attacks on Thursday and decided to release its advisory immediately, which appeared late on Friday.

FireEye said it had previously notified Microsoft of the issue and was coordinating disclosure with the release of a patch, but issued its advisory after the problem was made public.

Microsoft confirmed it is planning to fix the issue in a patch set to be released with its scheduled monthly update on Tuesday.

Experts advised users to avoid opening Word documents from untrusted sources and to apply the patch when it becomes available.

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