https://www.theregister.co.uk/2018/04/04/microsoft_windows_defender_rar_bug/
A remote-code execution vulnerability in Windows Defender – a flaw that can be exploited by malicious .rar files to run malware on PCs – has been traced back to an open-source archiving tool Microsoft adopted for its own use.
[...] Apparently, Microsoft forked that version of unrar and incorporated the component into its operating system's antivirus engine. That forked code was then modified so that all signed integer variables were converted to unsigned variables, causing knock-on problems with mathematical comparisons. This in turn left the software vulnerable to memory corruption errors, which can crash the antivirus package or allow malicious code to potentially execute.
(Score: 0) by Anonymous Coward on Monday April 09 2018, @09:21PM
That's not the unrar license, although it includes parts of it. A web search turned up this copy of the license text [fedoraproject.org], which matches what is found in tar file you can download from rarlab.com.
Note that there are actual free unpackers for the RAR formats (e.g., libarchive) so there is no reason to use the proprietary unrar.