Apple has released Safari 5.0.2 and Safari 4.1.2 to address vulnerabilities in WebKit. Users should apply these updates since they are both critical. There was an input validation issue related to floating point data types which could be exploited, this has been addressed by performing improved validation.
The other major issue is related to run-in styling which a malicious site could tag advantage of a use after free event. Object pointers has been improved in WebKit handling of run-in styling. Both of these updates require a restart of the server and client versions of MacOSX.