CVE-2017-15918: Sera 1.2 local root privesc and password disclosure

["Mark Wadham" <fd () rkw io>]

Sera is a free app for mac and iOS that lets you unlock your mac 
automatically
when your iphone is within a configured proximity.

Unfortunately to facilitate this it stores the users login password in 
their
home directory at:

~/Library/Preferences/no.ignitum.SeraOSX.plist

This makes root privilege escalation trivial and worse than that even
facilitates dumping the keychain as we can easily obtain the user's 
login
password. If they are an admin user we can even dump items from the 
system
keychain.

The author of Sera has said he will shut the project down and make the 
code
publicly available so no fix is likely to be forthcoming anytime soon.

It is strongly recommended not to use this app and if you have done so 
in the
past make sure you remove this file that contains your login password.

Proof of concept exploit here:

https://m4.rkw.io/blog/cve201715918-sera-12-local-root-privesc-and-password-disclosure.html

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