Fixing dangerous MIDI files

Ever visited a Web site that suddenly started playing music through your computer speakers? It may be annoying, but you can always turn down the volume. And it's harmless, right? Maybe not.

Researchers at EEye Digital Security Inc. recently discovered two big holes in Windows' music playback technology. The flaws, which Microsoft rates as "critical," could allow a hacker's code to run amok on your PC by exploiting a contaminated music file. The hacker could then take over your PC and do something nasty, like delete your files.

The problems lie in the way that Windows plays back a common type of music file called a MIDI (Musical Instrument Digital Interface) file. Unlike an audio file, a MIDI file contains a string of code that tells a synthesizer (such as the ones in most PCs) how to play a piece of music.

Microsoft Corp.'s DirectX technology, which handles playback for audio and video in Internet Explorer and in Windows Media Player, also plays MIDI files. Microsoft realized that it had left two unchecked buffers in versions of DirectX from Windows XP all the way back to Windows 98. This weakness could let a miscreant send a malformed MIDI file containing too much data to one of the buffers. And for that to happen, you just have to visit a booby-trapped Web site or open (or preview) an HTML e-mail message with an embedded link. This triggers the infected MIDI file to download to your PC. When the buffer overflows, DirectX malfunctions and the hacker's code starts to execute.

Take care of the hole by grabbing the latest version of DirectX, 9.0b. Head to the Microsoft bulletin, "Unchecked Buffer in DirectX Could Enable System Compromise," for more details and a link to the patch, and go to for EEye's bulletin.

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