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Vulnerability Assessment Details

NIDS evasion

Vulnerability Assessment Summary
NIDS evasion options

Detailed Explanation for this Vulnerability Assessment

This test configures Nessus for NIDS evasion (see the 'Prefs' panel).
NIDS evasion options are useful if you want to acertain
the quality of the expensive NIDS you just bought.

TCP Evasion techniques :
- Split : send data one byte at a time. This confuses
NIDSes which do not perform stream reassembly

- Injection : same as split, but malformed TCP packets
containing bogus data are sent between normal packets.
Here, a 'malformed' tcp packet means a legitimate TCP packet
with a bogus checksum.
This confuses NIDSes which perform stream reassembly but do
not accurately verify the checksum of the packets or
which do not acertain if the remote host actually
receives the packets seen


- Short TTL : same as split, but a valid TCP packets
containing bogus data are sent between normal packets.
These packets have a short (N-1), meaning that if
the NIDS is on a gateway, it will see these packets
go through, but they will not reach the target
host.
This confuses NIDSes which perform stream reassembly
but do not accurately check if the packet can actually
reach the remote host or which do not acertain if the
remote host actually receives the packets seen


- Fake RST : each time a connection is established, Nessus
will send a RST packet with a bogus tcp checksum or
a bogus ttl (depending on the options you chose above),
thus making the IDS believe the connection was closed
abruptly.
This confuses badly written NIDSes which believe
anything they see.

Warning: those features are experimental and some
options may result in false negatives!
This test does not do any security check.

Network Security Threat Level: None

Networks Security ID:

Vulnerability Assessment Copyright: This script is Copyright (C) 2002 Michel Arboi / Renaud Deraison

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