Dear Hugo van der Kooij,

--Friday, July 23, 2004, 10:21:22 PM, you wrote to bugtraq (at) securityfocus (dot) com [email concealed]:

HvdK> Both as NitroEngine or CVP server they will push as much of 80% to the
HvdK> end-user before they stop a virus. Then they rely on the adding of the
HvdK> exact URL so that URL can be blocked in all next requests.

It depends on how antiviral check is actually implemented. If connection
is broken immediately after signature is detected - there is no way to
download infected file, because signature will not pass to client and
client will not be able to use "Range:" header to resume partially
downloaded file.

If antiviral filter checks data _after_ all data received from client
with 20% buffering yes, it's possible to bypass this check for HTTP,
because there is no way (at least for HTTP/1.0 and FTP) to indicate
error to client and make him to delete partially downloaded data.

You can check it, by sending EICAR with some additional data: if you can
find EICAR signature on the client after connection is broken by
antiviral filter you can bypass it's protection.

--
~/ZARAZA
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