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Potentially malicious WinRAR vulnerability patched after almost 20 years

WinRAR is a powerful archival tool that has been available for the past 23 years, allowing users to unpack and create RAR, ZIP, and other archive files. But recently, a collection of security researchers at Check Point Software Technologies have discovered that a vulnerability that could allow malicious individuals to take advantage of users’ machines running the software, implanting startup programs without any needed authorization from the user.

Most users who had used WinRAR around the turn of the century most likely remember the software for its 40-day trial that could easily be bypassed — allowing for continuous use after the initial trial period. WinRAR still exists today, which is why the company quickly patched its software after learning about the vulnerability, adding a fix in version 5.7 beta 1 for an update that is long overdue.

The exact details of the dangerous vulnerability came down to a single DLL file — files used by Windows to access libraries of digital information  — that enabled exploiters to use an old component from the defunct ACE archive format. The ACE archive format was last updated in 2007, but WinRAR had decided to continue support for the format until now.

By merely renaming an ACE archive file extension to RAR, WinRAR can be manipulated to extract a malicious program into the computer’s startup folder. Using the exploit, the archive file would appear to decompress and extract itself as usual, while at the same time, in the background, inserting its contents into system folders. Instead of attempting to fix the particular issue, the team at WinRAR have instead dropped support for ACE archives.

Archiving files has come a long way since the world of ACE, and most users will find both the RAR and ZIP file formats to be much more effective than their older sibling. The software is still available on the web for anyone who may have older ACE files to extract or compress, but current Windows users using WinRAR will need to move forward in time if they wish to stay with their archive software of choice.

The ACE vulnerability existed for almost 20 years, with over 500 million WinRAR users, without being patched; it practically begs the question, if we all paid for the trial — would this have ever happened?

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