WoWDB

This pet comes from using the Rodent crate (Horde - Alliance) which costs 2000 of the respective factions commissions.

Placing the crate will summon lots of rodents swarming the area around it, staying for 20 minutes. There are plenty of them and they respawn quickly. The rodent is lv25 and accompanied by two more lv25 pets. As with all other wild pets, the quality is random, but with some tenacity you should be able to find one (by engaging/retreating).