full-disclosure - GAYER THAN AIDS ADVISORY #01: IE 5 remote code execution

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From: gta at hush.com (gta@...h.com)
Subject: GAYER THAN AIDS ADVISORY #01: IE 5 remote code execution

I downloaded the Microsoft source code.  Easy enough.  It's a lot
bigger than Linux, but there were a lot of people mirroring it and so
it didn't take long.

Anyway, I took a look, and decided that Microsoft is GAYER THAN AIDS.
For example, in win2k/private/inet/mshtml/src/site/download/imgbmp.cxx:

    // Before we read the bits, seek to the correct location in the file
    while (_bmfh.bfOffBits > (unsigned)cbRead)
    {
        BYTE abDummy[1024];
        int cbSkip;

        cbSkip = _bmfh.bfOffBits - cbRead;

        if (cbSkip > 1024)
            cbSkip = 1024;

        if (!Read(abDummy, cbSkip))
            goto Cleanup;

        cbRead += cbSkip;
    }

.. Rrrrriiiiggghhhttt.  Way to go, using a signed integer for an
offset.  Now all we have to do is create a BMP with bfOffBits > 2^31,

and we're in. cbSkip goes negative and the Read call clobbers the
stack with our data.

See attached for proof of concept.  index.html has [img src=1.bmp]
where 1.bmp contains bfOffBits=0xEEEEEEEE plus 4k of 0x44332211.
Bring it up in IE5 (tested successfully on Win98) and get
EIP=0x44332211.

IE6 is not vulnerable, so I guess I'll get back to work.  My Warhol
worm will have to wait a bit...

.gta
PROPS TO the Fort and HAVE IT BE YOU.

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