There is no single industry-standard plugin named exactly "Flex Morph" that works like a morphing pitch/formant shifter (similar to Polyverse Manipulator or Elastique Pitch) available for legitimate free download as cracked software. Downloading cracked VSTs is the #1 way to get ransomware, keyloggers, or botnet malware.
The full commercial version of the Re Flex Morph Plugin is typically a paid product (retailing around $99). However, the developers offer a legitimate free trial and, in partnership with several music tech blogs, a limited "Lite" version that is 100% free and legal.
RE:Flex is widely considered an industry standard because it uses the host application's native spline and masking tools to direct transformations rather than complex, rigid meshes.
RE:Flex is proprietary, commercial software. A single license currently costs several hundred dollars (prices vary by vendor and sale periods). There is no legitimate "freeware" version of the full plugin.