Re: Remote crash in tcpdump from OpenBSD

[Balaram Amgoth <ramgoth () yahoo com>]

In-Reply-To: <20031221174837.14808.qmail () sf-www3-symnsj securityfocus com>

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";

Thanks for your time in advance

Balaram



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> From: <mrh_tech () yahoo com>
> To: bugtraq () securityfocus com
> Subject: Re: Remote crash in tcpdump from OpenBSD
>
> In-Reply-To: <3FE4CAC1.8010306 () freebsd lublin pl>
>
> 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