Without /dev/urandom being available to read the medium RNG will rely only on the following components on a Linux system:
1. MicroTime: microtime() . memory_get_usage() as seed and then a garbage collected microtime for loop
2. MTRand: chr((mt_rand() ^ mt_rand()) % 256)
3. Rand: chr((rand() ^ rand()) % 256)
4. UniqId: Plain uniqid()
An adversary with the possibility to predict the seed used by the PHP process may thus be able to predict future tokens which is an unwanted behaviour.
One should note that this behaviour is documented in our documentation to ensure that users get aware of this even without reading our documentation this will add a post setup check to the administrative interface.
Thanks to David Black from d1b.org for bringing this again to our attention.
Doing this in the PHP code is not the right approach for multiple reasons:
1. A bug in the PHP code prevents them from being added to the response.
2. They are only added when something is served via PHP and not in other cases (that makes for example the newest IE UXSS which is not yet patched by Microsoft exploitable on ownCloud)
3. Some headers such as the Strict-Transport-Security might require custom modifications by administrators. This was not possible before and lead to buggy situations.
This pull request moves those headers out of the PHP code and adds a security check to the admin settings performed via JS.
*Changes:*
* "… is not yet properly setup" in line 24 is changed to " … is not yet set up properly" (better word order and space in the middle of "set up", as it is a participle of the verb "to set up").
* "internet" is corrected to "Internet" with a capitalized "I" in lines 54 and 59.
* Also in line 54: "3rd party" is changed to "third-party" to for a more coherent spelling across the different ownCloud components.
* "… apps don´t work" is corrected to "… apps won't work" (with a proper (and hopefully correctly escaped) (apostrophe)[http://en.wikipedia.org/wiki/Apostrophe#Typographic_form] instead of the (acute accent)[http://en.wikipedia.org/wiki/Acute_accent]).
* Still in line 54: The negation is corrected from "… might also not work" to "… might not work, either".
- Added setup checks in JavaScript
- Moved isWebDAVWorking to JS using SetupChecks
- Moved internet connection checks to an ajax call that goes through the
server
Lukas Reschke
Joas Schilling
cmeh
Vincent Petry