The key vulnerability stemmed from improper path resolution when handling hardlinks during extraction. The commit 0667282 shows the fix changed from path.resolve(cwd, header.linkname) to path.join(cwd, path.join('/', header.linkname)), which prevents path traversal by normalizing the link target path relative to the extraction directory. This function was directly responsible for validating() hardlink targets, and its lack of proper input validation allowed overwriting arbitrary existing files through specially crafted tarballs.