This affects the package npm-user-validate before 1.0.1. The regex that validates user emails took exponentially longer to process long input strings beginning with @ characters.
https://github.com/npm/npm-user-validate/security/advisories/GHSA-xgh6-85xh-479p
https://github.com/npm/npm-user-validate/commit/c8a87dac1a4cc6988b5418f30411a8669bef204e