OwnCloud is using Mersenne Twister (not secure) seeded by time of day and PID (which is not nearly enough entropy) to generate keys. The encryption is done in ECB mode, which leaks data (https://en.wikipedia.org/wiki/Block_cipher_modes_of_operatio...). The encryption key is stored in the clear in session data, which usually resides in /tmp.

There's more, but those seem to be the worst parts.

Also, what's the benefit of using a 7-year-old pure-PHP implementation of Blowfish when mcrypt gets the job done much better and faster? OwnCloud's install instructions actually require a bunch of PHP extensions. They could have just thrown mcrypt into that list.

passwords stored in the clear in server-side sessions => server hack compromises data. storing keys server-side means admins can get into your data.

had a big lol at the use of blowfish ECB - use of any cipher's ECB mode for bulk encryption is asking for problems. they should be using CBC, CTR, LRW or, ideally, XTS modes.