If you think you have discovered a security issue, please report it through the project issue tracker New issue as a confidential issue (select confidential checkbox).
An alternative is to send PGP encrypted mail to the cryptsetup maintainer. Current maintainer is Milan Broz, use PGP key with fingerprint 2A29 1824 3FDE 4664 8D06 86F9 D9B0 577B D93E 98FC.