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Friday, 28 June 2019 12:01

Microsoft refuses to fix Excel bug that can be used to plant malware

Microsoft refuses to fix Excel bug that can be used to plant malware Image by Christian Dorn from Pixabay

Microsoft has refused to fix a vulnerability in its Excel spreadsheet, which has about 120 million users worldwide, after the email security provider Mimecast informed the software giant that the Power Query tool could be used to embed malicious content in an Excel document.

Mimecast Security Research Team leader Ofir Shlomo said in a blog post that the Power Query tool could be used to launch a remote dynamic data exchange attack into an Excel spreadsheet and control the payload.

Explaining the loophole, to which researcher Doron Attias had contributed, Shlomo wrote: "Power Query is a powerful and scalable business intelligence tool that lets users integrate their spreadsheets with other data sources, such as an external database, text document, another spreadsheet, or a web page, to name a few.

"When sources are linked, the data can be loaded and saved into the spreadsheet, or loaded dynamically (when the document is opened, for example)."

He said research had shown that Power Query could be used to embed malicious content in a separate data source; the content was loaded into the spreadsheet when it was opened and the malicious code was used to plant malware on the user's machine.

"The feature gives such rich controls that it can be used to fingerprint a sandbox or a victim’s machine even before delivering any payloads, Shlomo said.

"The attacker has potential pre-payload and pre-exploitation controls and could deliver a malicious payload to the victim while also making the file appear harmless to a sandbox or other security solutions."

But Microsoft refused to release a fix for this issue and only outlined a workaround to mitigate the bug, namely to either use a Group Policy to block external data connections or use the Office Trust centre to achieve the same outcome.

"Attackers are looking to subvert the detections that victims have," Shlomo said.

"While there is a chance that this kind of attack may be detected over time as threat intelligence is shared between various security experts and information sharing platforms, Mimecast strongly recommends all Microsoft Excel customers implement the workarounds suggested by Microsoft as the potential threat to these Microsoft users is real and the exploit could be damaging."

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Sam Varghese

Sam Varghese has been writing for iTWire since 2006, a year after the site came into existence. For nearly a decade thereafter, he wrote mostly about free and open source software, based on his own use of this genre of software. Since May 2016, he has been writing across many areas of technology. He has been a journalist for nearly 40 years in India (Indian Express and Deccan Herald), the UAE (Khaleej Times) and Australia (Daily Commercial News (now defunct) and The Age). His personal blog is titled Irregular Expression.

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