bugtraq - Re: Skype callto:// BoF technical details

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Message-ID: <004c01c4cc1b$db730cb0$0100a8c0@grotedoos>
Date: Tue, 16 Nov 2004 21:35:44 +0100
From: "Berend-Jan Wever" <skylined@...p.tudelft.nl>
To: "Fabian Becker" <neonomicus@....de>
Cc: <bugtraq@...urityfocus.com>, <full-disclosure@...ts.netsys.com>
Subject: Re: Skype callto:// BoF technical details


It is the same bug as far as I know.

Cheers,
SkyLined

----- Original Message ----- 
From: "Fabian Becker" <neonomicus@....de>
To: "Berend-Jan Wever" <skylined@...p.tudelft.nl>
Cc: <bugtraq@...urityfocus.com>; <full-disclosure@...ts.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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