The QNAP TS-239 Pro and TS-639 Pro with firmware 2.1.7 0613, 3.1.0 0627, and 3.1.1 0815 create an undocumented recovery key and store it in the ENCK variable in flash memory, which allows local users to bypass the passphrase requirement and decrypt the hard drive by reading this variable, deobfuscating the key, and running a cryptsetup luksOpen command.