The first thing I found on Google for East Germany is this. It deals with multiple cashiers at the East German State Bank allowing Soviet citizens (soldiers, tourists, railway personnel) to change more Rubles than allowed into East German Mark and getting an 8% share.
This went on over several years, but apparently did not lead to legal proceedings in order to avoid negative publicity. Especially since certain Soviet military members stationed in East Germany were involved.
As the other answers point out, corruption was common in socialist countries. If you search the web in the relevant languages, you will probably find lots and lots of concrete examples.
Probably some of the reasons for this prevalence of corruption had to do with the inefficienciey of a central planning economy. E.g. if certain important goods are hard to get for private citizens, but easy to obtain for state-owned enterprises, such goods will often inofficially turn from enterprise property into private property. Often this was done out of sheer necessity. But if you do this once out of necessity, the next time you might do something similar for convenience, and a third time for financial gain.