Re: Skype callto:// BoF technical details

From: Berend-Jan Wever (skylined_at_edup.tudelft.nl)
Date: 11/16/04

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    To: "Fabian Becker" <neonomicus@gmx.de>
Date: Tue, 16 Nov 2004 21:35:44 +0100

    It is the same bug as far as I know.

    Cheers,
    SkyLined

    ----- Original Message -----
    From: "Fabian Becker" <neonomicus@gmx.de>
    To: "Berend-Jan Wever" <skylined@edup.tudelft.nl>
    Cc: <bugtraq@securityfocus.com>; <full-disclosure@lists.netsys.com>
    Sent: Tuesday, November 16, 2004 20:50
    Subject: Re: Skype callto:// BoF technical details

    > 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 :)
    >
    >

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