bugtraq - Re: Remote crash in tcpdump from OpenBSD

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Message-ID: <20040806074142.25093.qmail@www.securityfocus.com>
Date: 6 Aug 2004 07:41:42 -0000
From: Balaram Amgoth <ramgoth@...oo.com>
To: bugtraq@...urityfocus.com
Subject: Re: Remote crash in tcpdump from OpenBSD


In-Reply-To: <20031221174837.14808.qmail@...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@...oo.com>
>To: bugtraq@...urityfocus.com
>Subject: Re: Remote crash in tcpdump from OpenBSD
>
>In-Reply-To: <3FE4CAC1.8010306@...ebsd.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
>
>
>