According to security researcher David Emry, users who used FileVault prior to upgrading to 10.7.3 may be able to find their password in a system-wide debug log file, stored in plain text outside of the encrypted area.



From Engadget:

This puts the password at risk of being read by other users or enterprising cyber criminals, Emry explains, and even opens the door for new flaw-specific malware. FileVault 2, on the other hand, seems to be unaffected by the bug. The community doesn't currently have a way to fight the flaw without disabling FileVault, so users rushing to change their password now may find it being logged as well.

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