Re: Remote crash in tcpdump from OpenBSD

[Otto Moerbeek <otto@xxxxxxxxx>]

On Fri, 6 Aug 2004, Balaram Amgoth wrote:

> In-Reply-To: <20031221174837.14808.qmail@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi Mike,
> Will the following packet be enough to reproduce this problem.
>
> char packet[] = "\x82\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00";

FYI, this is a report from December 2003. This has been fixed in OpenBSD
3.4-stable and (then -current, now) 3.5. Feel free to expore this further, 
but I don't think this is very interesting material for this list, more 
than 7 months after the original report.

        -Otto

> Thanks for your time in advance
>
> Balaram
>
>
>
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> > From: <mrh_tech@xxxxxxxxx>
> > To: bugtraq@xxxxxxxxxxxxxxxxx
> > Subject: Re: Remote crash in tcpdump from OpenBSD
> >
> > In-Reply-To: <3FE4CAC1.8010306@xxxxxxxxxxxxxxxxx>
> >
> > When an l2tp control packet is sent with optional bits set but containing 
> > invalid data, l2tp_avp_print() is passed this bad data.
> > Then, l2tp_avp_print() calls itself and continues an infinite loop of passing 
> > bad data to itself.
> >
> > I had the consistent results sending:
> > \x82 (control+length bits)
> > \0x02 (version) then 10 bytes of zeros.
> >
> > This is in print-l2tp.c
> > Lines: ~566-616
> >
> > After commenting out (breaking the infinite loop):
> > ~609: l2tp_avp_print(dat + len, length - len);
> > I was no longer able to crash tcpdump.
> >
> > Obviously, properly validating the input is the real solution.
> >
> > Tested on: OpenBSD 3.3 and 3.4
> > tcpdump: 3.4.0
> > libpcap" 0.5
> >
> > Thanks,
> > Mike