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Re: Remote crash in tcpdump from OpenBSD
Dec 21 2003 05:48PM
mrh_tech yahoo com
In-Reply-To: <3FE4CAC1.8010306 (at) freebsd.lublin (dot) pl [email concealed]>
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
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
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