Re: Skype callto:// BoF technical details

From: Fabian Becker (neonomicus_at_gmx.de)
Date: 11/16/04

  • Next message: Berend-Jan Wever: "Re: Skype callto:// BoF technical details" 
    Date: Tue, 16 Nov 2004 20:50:07 +0100
To: Berend-Jan Wever <skylined@edup.tudelft.nl>

    Berend-Jan Wever wrote:

    >Skype reported they've found a remotely exploitable BoF in the callto:// URI handler. New version has been released.
    >http://www.skype.com/products/skype/windows/changelog.html
    >http://secunia.com/advisories/13191/
    >
    >Technical details:
    >
    >The bufferoverflow happens when a skype user clicks on a "callto://username" link with a username longer then 4096 characters that does not exist: An error message is created and put into a buffer without correct size checks. The errormessage and buffer are unicode but unicode characters are filtered out and replaced with '?'. Only printable ascii characters seem to get through. A return address can be overwritten as well as the SEH. Exploitation is complicated by the fact that return addresses have to be in range 0x00??00??.
    >
    >Webbrowsers like MSIE do not support URI's long enough to trigger the BoF. To exploit it, one could send a skype user a callto:// link in a private message and trick him/her into clicking it.
    >
    >If one would want to, one could write a skype worm with this. User interaction would be required: they'd have to click the link.
    >
    >Cheers,
    >SkyLined
    >
    >
    >
    >
    >
    They fixed it without knowing of the callto:// thing I suppose cause I
    wrote them an email saying that the quick-call field is exploitable,
    too. This was fixed within the new version. Maybe your flaw is fixed,
    too, if not, I think it soon will be :)

  • Next message: Berend-Jan Wever: "Re: Skype callto:// BoF technical details"

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