Bad guys have something new to play with! Microsoft Excel adds support for JavaScript

There may be trouble ahead…

Bad guys have something new to play with! Microsoft Excel adds support for JavaScript

Microsoft has launched some new features in its Excel spreadsheet software that will boost its power. But will that only be for the benefit of users?

In its blog post about the new functionality, Microsoft says that there are “many reasons” why people might be interested in writing JavaScript custom functions, and gives the following examples:

  • Calculate math operations, like whether a number is prime.
  • Bring information from the web, like a bank account balance.
  • Stream live data, like a stock price.

Hmm… Yes, well, I can think of a few more examples that maliciously-minded developers might be keen to try out.

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But hey, nothing bad could come of this, surely!

Note: The Excel JavaScript custom functions “feature” is currently available in the Developer Preview edition to Office 365 subscribers enrolled in the Office Insiders program. Presumably in the fullness of time it will be rolled out to all users.

See also: Cryptomining with JavaScript in an Excel spreadsheet

Graham Cluley is an award-winning keynote speaker who has given presentations around the world about cybersecurity, hackers, and online privacy. A veteran of the computer security industry since the early 1990s, he wrote the first ever version of Dr Solomon's Anti-Virus Toolkit for Windows, makes regular media appearances, and is the co-host of the popular "Smashing Security" podcast. Follow him on Twitter, Mastodon, Threads, Bluesky, or drop him an email.

3 comments on “Bad guys have something new to play with! Microsoft Excel adds support for JavaScript”

  1. Crypiehef

    Any readers know if Microsoft will have a group policy to disable the feature?

  2. PEM

    This new inherent risk is just piling on at this point. Many organizations don't even have a way to keep an up-to-date inventory of financially-significant and operationally-significant spreadsheets, much less protect them from accidental or malicious alterations. As the 'killer app', the spreadsheet in used nearly everywhere to support decisions and feed financial systems, yet remains a weak link in data protection.

  3. THH

    PEM – is spot on with his comment.

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