Don't think that the Bengals are completely ignoring possible roster additions at cornerback; they're just not interested in signing big-name players that would make an immediate impact, believing that the players in the building are just as good as anyone that's available. But they are looking.
According to Joe Reedy with the Cincinnati Enquirer, the Bengals placed a waiver claim on cornerback Jordan Poyer, who was cut by the Philadelphia Eagles to make room for running back Matthew Tucker on the team's active roster.
Waivers are like the NFL draft. When a player is placed on waivers, every team has the opportunity to submit a claim on that player. The team with the worst record (think draft order) that placed a claim, will receive that player.
Unfortunately for the Bengals, the Browns also placed a claim on Poyer and Cleveland was awarded the rookie cornerback on Monday. Poyer is a former seventh-round pick by the Eagles during the 2013 NFL draft, playing three games in Philadelphia and recording three tackles.