The large company at which Sela works, uses badges with a magnetic stripe for entry access. Which threat model should Sela be concerned about with badges like these?

Sela should be worried about cloning the badges because magnetic stripe badges are relatively simple to clone in most cases. Tailgating is popular, particularly if there are large numbers of staff, since staff are unlikely to allow doors to close and then reopen them for every individual who enters during shift changes. Since magnetic stripe readers don’t require any additional information, use by unauthorized individuals is easy if a badge is lost or stolen.