NETSED man page on Kali
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NETSED(1) NetSED NETSED(1)
NAME
netsed - a network stream editor.
SYNOPSIS
netsed {proto} {lport} {rhost} {rport} {rule} [rule ...]
DESCRIPTION
netsed is a small and handy utility to alter, in real time, the
contents of packets forwarded in a network stream, or in a datagram
connection. When called with a set of replacement rules, these rules
are tested for applicability to each packet entering in either
direction.
ARGUMENTS
proto
Determines the protocol for the desired connection: "tcp", "TCP",
"udp", or "UDP".
lport
The local listening port for the connection. A service name, or a
numerical port value, is acceptable.
rhost
The remote host with whom the connection is desired. Resolvable
host names and IPv4/IPv6 addresses are equally usable.
As a special case, assigning "0" to rhost will insert the kernel's
knowledge of the targeted host address, in a situation where a
netfilter rule is redirecting traffic. This happens when running a
transparent proxy service.
rport
The remote port to connect to. A service name, or a numerical port
value, is acceptable.
Also here a value "0" will be acceptable to arrange a transparent
proxy service, as the kernel's tracking will provide the intended
remote port number.
rule
At least one replacement rule is mandatory. The general syntax for
this is:
s/pat1/pat2[/flag]
The effect is to replace the text that matches pat1 with the
expansion of pat2. The optional parameter flag is a composite
containing a numerical value limiting the maximal number of times
the rule can be applied, or a direction semaphore indicating that
the rule applies only to incoming (coded as 'I' or 'i') or outgoing
('O' or 'o') traffic. One could say that the rule expires after num
occurrences.
The rules are applied in succession to all passing packets, flowing
in either direction. As soon as a rule has been expired, it is
removed from the collection of active rules for the current
connection. Observe that any counter is started as the connection
is initiated, running as long as the connection is alive.
This holds directly for TCP connections, whereas for UDP a
connection is considered to consist of incoming data on fixed
address and fixed port together with any response from a remote
server. When no datagrams have been transmitted for a period of 30
seconds, the UPD connection is seen as closed.
A single rule is limited to act on individual packets; a pattern
can not match across packet boundaries.
Using HTTP-like escape sequences for hexadecimal values, all
eight-bit characters are viable in the patterns. Thus the standard
character pair CRNL would code as "%0a%0d". In a pattern, the
percentage sign itself must be escaped by duplication. Thus a
string "%%" is interpreted in a pattern as a literal percentage
sign.
EXAMPLES
A handful replacement rules are handy as examples.
s/andrew/mike
Replace every occurrence of the string "andrew" with "mike", in
every passing packet.
s/andrew/mike/1
Replace only the first occurrence of the string "andrew" for "mike"
in each packet. Any repetition is unaltered, unless a further rule
specifies some replacement.
s/andrew/mike%00%00
Replace in each packet every occurrence of the string "andrew" with
"mike\x00\x00" . The padding with two null bytes ensures an
unaltered packet length, which might be essential at times.
s/%%/%2f/20
Replace the first twenty occurrences of the percentage character
'%' with slashes '/'.
s/Rilke/Proust/o, s/Proust/Rilke/i
Let Rilke travel incognito as Proust, i.e., on outgoing packets
replace Rilke's real sirname by Proust, then restore it again in
any incoming packet.
AUTHOR
This text was initially compiled by Mats Erik Andersson as a Docbook
source from the usage printout. Permission is granted to copy,
distribute and/or modify this document under the terms of the GNU
General Public License, version 2, or of a later version.
COPYRIGHT
Copyright © 2010-2014 Mats Erik Andersson
NetSED 1.2 May 23rd, 2014 NETSED(1)
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