Microsoft Silverlight 5 suffers from invalid typecast and memory disclosure vulnerabilities that, when leveraged together, allow for arbitrary code execution. A memory disclosure vulnerability exists in the public WriteableBitmap class from System.Windows.dll. This class allows reading of image pixels from the user-defined data stream via the public SetSource() method. BitmapSource.ReadStream() allocates and returns byte array and a count of array items as out parameters. These returned values are taken from the input stream and they can be fully controlled by the untrusted code. When returned "count" is greater than "array.Length", then data outside the "array" are used as input stream data by the native BitmapSource_SetSource() from agcore.dll. Later all data can be viewed via the public WriteableBitmap.Pixels[] property. Exploitation details related to these findings were purchased through the Packet Storm Bug Bounty program.
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