A firewall problem?

Sarad AV jtrjtrjtr2001 at yahoo.com
Fri Jul 4 01:55:43 PDT 2003


Wont the following cause a firewall breach-

First we capture   inbound packets to a firewall
assuming we have a man in the middle(M).

If (M) use block replay on packets he can inject bits
and pieces of his own information to an inbound
firewall and can go undetected?

M doesn't alter the source and destination ip's and is
perfectly acceptable to the firewall.Even a timestamp
won't work since a packet is expected at any time.

We can still re-calculate the CRC of Checksum field by
the same attack and replace the old crc/checksum after
changing various required bit positions.

Do firewall programs use initialisation vectors and a
chaning mode to prevent this attack?

Regards Sarath.

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