Re: Skype callto:// BoF technical details

["Berend-Jan Wever" <skylined () edup tudelft nl>]

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 :)