iDefense Security Advisory 07.18.07 - Exploitation of an input validation vulnerability in Microsoft Corp.'s DirectX library could allow an attacker to execute arbitrary code in the context of the current user. The vulnerability specifically exists in the way RLE compressed Targa format image files are opened. The Targa format allows multiple color depths and image storage options, depths and image storage options, and includes the ability to use run-length encoding (RLE), compression on the image data. This is a compression method which finds a 'run' of the pixels the same color and instead of storing the value multiple times, encodes the number of times to repeat one value. For example, instead of storing 'AAAAAAAA', it may encode that into 'store "A" 8 times'. The buffer allocated for the image data is based on the width, height and color depth stored in the image, but when decoding this type of file, no checks against writing past the end of the buffer are performed. If the encoding specifies more data than has been allocated, a controlled heap overflow can occur. iDefense has confirmed that libraries in Microsoft's DirectX SDK (February 2006) are vulnerable, as are the DirectX End User Runtimes (February 2006). It is suspected that previous versions are also affected, including the DirectX 9.0c End User Runtimes.
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