Upvote:3
There are several sites to look up PNRs that are run by the major GDS (Global Distribution System) providers. While I cannot vouch for their security, they are run by the same companies that run the ticketing systems, and are therefore more likely to be reliable than mere "random websites":
Not all airlines use these systems and not all reservations are visible through these sites, so there's no guarantee you'll find your PNR, but it's worth a try.