There are certain platforms where gamers can find cheap CD keys but in most cases they work as intermediaries. For example, in the case of G2A, code for some games may be sold by an individual who does not intend to use them. Some websites also offer CD keys for very cheap prices because the games are recycled. There are also categories by consoles and themes that make the CD keys cheaper to buy.
Artem Moskowsky recently discovered vulnerability in the development portal of Valve Steam that can be exploited to reveal every license key for the all games that are available in the platform. Moskowsky could have easily exploited the vulnerability and earned a profit by selling the keys but he chose to report the findings to Valve. He was awarded with $20,000 for discovering the vulnerability.
The bug was discovered by Moskowsky in August but it was only recently that Valve announced that they have fixed the flaw and guaranteed that it will never be exploited again. Actually, Moskowsky accidentally stumbled on the bug while he was taking a stroll on the developer site of Valve. The site is a platform where game sellers manage their titles.
According to The Register, Moskowsky noticed that it was rather easy to change the parameters in an API request and obtain activation keys for a selected game. The keys which are more popularly known as CD keys are used to activate and play games that have been downloaded from Steam. API is provided to allow developers and their partners to obtain license keys to the titles they pass to gamers.
Any attacker could have obtained access to the portal after exploring the functionality of the web application. Moskowsky was able to bypass verification of ownership of the game by simply changing one parameter. Once an ID has been entered into another parameter, any set of keys can be taken.
There are many ways to find cheap CD keys from resellers to promotional deals. Since games are available in global platforms, you can search for specific countries that have weaker currencies. You can also use comparison sites to start the hunt for cheap games.