bugtraq - Re: Remote crash in tcpdump from OpenBSD

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Date: Sat, 7 Aug 2004 20:45:30 +0200 (CEST)
From: Otto Moerbeek <otto@...jf.net>
To: Balaram Amgoth <ramgoth@...oo.com>
Cc: bugtraq@...urityfocus.com
Subject: Re: Remote crash in tcpdump from OpenBSD




On Fri, 6 Aug 2004, Balaram Amgoth wrote:

> 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";

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@...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
>>
>>
>>
>
>