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Microsoft Releases Patch For Microsoft Word Zero-Day Spreading Dridex Malware

Last week, a zero-day vulnerability has been found that was used to spread the Dridex banking trojan. A Microsoft patch was released last Tuesday to address this.

The said vulnerability has been spreading using a massive spam campaign which contains a Microsoft Word documents. The Word document exploited the vulnerability utilizing the way it handles OLE2Link objects. It has been determined that it was effective in bypassing mitigation efforts.

Fortunately, the newest patch includes a fix for this vulnerability.

“This is the first campaign we have observed that leverages the newly disclosed Microsoft zero-day,” Proofpoint wrote in a technical analysis of the zero day. “This represents a significant level of agility and innovation for Dridex actors.”

The email campaign utilizing Microsoft zero-day vulnerability, according to Proofpoint, was extremely effective.

Their security researchers have said that “When recipients open the document, the exploit–if successful–is used to carry out a series of actions that lead to the installation of Dridex botnet ID 7500 on the user’s system.”

“The Microsoft OLE2Link object can open application data based on the server-provided MIME type, which can allow an unauthenticated remote attacker to execute arbitrary code on a vulnerable system,” according an advisory released by the DHS-sponsored CERT hosted at the Software Engineering Institute at Carnegie Mellon University.

Mcafee was first on the scene and first reported it last Friday. Most cases of macro-laced documents attached to emails are blocked by Microsoft Office and Windows 10. However, this one does not have to enable the macrost to run the exploit.

Tests have been conducted by Security firm Proofpoint, and their test system has been exploited by just opening an Office 2010 document. Upon opening the document , users were presented with a dialogue box that asked “This document contains links that may refer to other files. Do you want to update this document with the data from the linked files?”

It is really alarming to know that once this dialogue box appears, the Dridex malware injection has already began.

The attack involves a Microsoft Office RTF document that contain an embedded OLE2link object. “When the user opens the document, winword.exe issues a HTTP request to a remote server to retrieve a malicious .hta file, which appears as a fake RTF file,” according to an analysis of the zero day by FireEye researchers.

The HTA application then loads and executes malicious scripts that halt the winword.exe loading process. Next, the scripts download payloads and load a decoy document for the user to see, according to FireEye.

“The original winword.exe process is terminated in order to hide a user prompt generated by the OLE2link,” FireEye researcher wrote.

“Clearly the fact that the RTF file is able download the malicious HTML that enables local execution of malware points to a lack of control in interpreting untrusted input from the outside world,” said Paul Farrington, manager of EMEA Solution Architects at Veracode. “The Microsoft engineers will not only need to devise a patch for this vulnerability, but also to remodel their threat assessment of this type of file interaction,” Farrington said.

The spam campaigns delivering the zero day spoofed the recipient’s domain in the sender’s email address and appear to be from either “copier”, “documents”, “noreply”, “no-reply”, or “scanner”. The subject line in all cases is “Scan Data” and included attachments named “Scan_123456.doc” or “Scan_123456.pdf” – with the numbers randomly generated.

The issue can infect a lot of computers due to the fact that the vulnerability affects Microsoft Office including the latest versions running on Windows 10.

Mitigation includes installing the Microsoft patch. However, Microsoft notes “you must have the release version of Service Pack 2 for Office 2010 installed on the computer” to apply the security update. Alternatively, security experts recommend blocking RTF documents in Microsoft Word via the File Block Settings in the Microsoft Office Trust Center. They also recommend using Microsoft Office Protected View, which they say can help prevent exploitation without user interaction.

Good thing that they have a patch to ease our minds, otherwise, it can become a huge security threat worldwide. A huge percentage of computer users use Microsoft Windows and Microsoft Office which makes it a very huge target waiting to get hit. Might as well do the suggested tips mentioned above like enabling Microsoft Office Protected View and blocking RTF documents in the Microsoft Trust Center.

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