high severity vulnerability
$ npm audit
┌───────────────┬──────────────────────────────────────────────────────────────┐
│ High │ Prototype Pollution │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Package │ set-value │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Dependency of │ grunt-cli [dev] │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Path │ grunt-cli > liftoff > findup-sync > micromatch > braces > │
│ │ snapdragon > base > cache-base > set-value │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ More info │ https://npmjs.com/advisories/1012 │
└───────────────┴──────────────────────────────────────────────────────────────┘
Strange on a fresh install I don't see that:

But [email protected] does get installed. Even when installing the latest liftoff so we might need wait for https://github.com/js-cli/js-liftoff/issues/107 to be resolved and then update here.
Something weird is going on. When I run npm audit against grunt-cli master branch, I get no warnings. But when I import grunt-cli 1.3.2 into another project, I get dozens of warnings for grunt-cli dependencies.
Regards liftoff, the project has lapsed. I published a fork with the security patches:
https://www.npmjs.com/package/liftoff2
Closing, because use of liftoff was temporary while issues with liftoff were addressed. https://github.com/gulpjs/liftoff has resumed maintenance since then, and is used by grunt-cli 1.4.2+.