unar is unable to unpack certain rar files, like: https://mega.nz/#!TZUGyKBI!5rITrOXUUBXaThpWfwxc_Hks-UI64eKi7O_336Vn4og

unar for other systems manages to unpack this file. The reason is one of the patches that our upstream (Debian) applies:

fix-crashes.patch
CSInputBuffer-bit-string-reading.patch
gnustep-support.patch
proper-init-autoreleasepool.patch

Other patches applied:

document-undocumented-options.patch
use-system-wavpack.patch
pass-cppflags-for-fortify-functions.patch
remove-build-date.patch

do not influence this issue.

I suspect that the most likely cause is the fix-crashes.patch patch, but I couldn't confirm this because the 4 patches need to be applied all together, else build or patching fails.

I suggest leaving out the first 4 patches (fix-crashes.patch, CSInputBuffer-bit-string-reading.patch, gnustep-support.patch and proper-init-autoreleasepool.patch) and to leave whatever fixes they do to the main developer of unar to implement.