Level 52
Content Creator
Malware Hunter
WinRAR, one of the world's most popular Windows file compression applications, has patched last month a severe security flaw that can be abused to hijack users' systems just by tricking a WinRAR user into opening a malicious archive.

The vulnerability, discovered last year by security researchers from Check Point Software, impacts all WinRAR versions released in the last 19 years.

On its website, the WinRAR team boasts of having a userbase of over 500 million users, all of whom are most likely impacted. The good news for all WinRAR users is that WinRAR devs released an update to fix the issue last month.

According to a Check Point technical write-up that takes a deep dive into WinRAR's inner workings, the vulnerability resides in the UNACEV2.DLL library included with all WinRAR versions.

This library is responsible for unpacking archives in the ACE format. Check Point researchers discovered a way to build malicious ACE archives that when decompressed used coding flaws in this library to plant malicious files outside the intended decompression path destination.
WinRAR devs released WinRAR 5.70 Beta 1 on January 28 to address this vulnerability --tracked under the CVE-2018-20250, CVE-2018-20251, CVE-2018-20252, and CVE-2018-20253 identifiers.

Download: WinRAR 5.70 Beta 1 32bit
Download: WinRAR 5.70 Beta 1 64bit


Level 7
The solution is simple:

1: update to 5.70 beta 1 if your license permits the update or
2. untick the .ace archive from being opened with winrar if you can`t update.


"Nadav Grossman from Check Point Software Technologies informed us about a security vulnerability in UNACEV2.DLL library. Aforementioned vulnerability makes possible to create files in arbitrary folders inside or outside of destination folder when unpacking ACE archives.

WinRAR used this third party library to unpack ACE archives. UNACEV2.DLL had not been updated since 2005 and we do not have access to its source code. So we decided to drop ACE archive format support to protect security of WinRAR users.

We are thankful to Check Point Software Technologies for reporting this issue. "



Level 17
Content Creator
2. untick the .ace archive from being opened with winrar if you can`t update.
There's also a file "Ace32Loader.exe" in the WinRAR folder. I'm not entirely certain of its function, but WinRAR seems to work without it (I renamed the extension).

Then update it?
No lifetime license here so I'm left with what I have. Funny, but the previous time I bought WinRAR a similar threat surfaced. So this one is on me :oops:
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Level 17
Content Creator
Oddly most of these articles pile on WinRAR when in fact most all ace-capable compressors share this vulnerability. For example...
Bandizip Version History

v6.21 Feb 23, 2019
  • Stopped ACE archive format support due to vulnerability (CVE-2018-20250)
  • Fixed: Crash problem while extracting specific NSIS
  • Fixed: Shell extension does not work for the specific case
  • Some minor bug fixes