Under the default configuration, Devise-Two-Factor versions >= 2.2.0 & < 6.0.0 generate TOTP shared secrets that are 120 bits instead of the 128-bit minimum defined by RFC 4226. Using a shared secret shorter than the minimum to generate a multi-factor authentication code could make it easier for an attacker to guess the shared secret and generate valid TOTP codes.
As a result of an incomplete fix for CVE-2015-7225, in versions of devise-two-factor prior to 4.0.2 it is possible to reuse a One-Time-Password (OTP) for one (and only one) immediately trailing interval. CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N)