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A suite for man in the middle attacks
Copyright 2001-2004 ALoR & NaGA
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Aoccdrnig to rscheearch at an Elingsh uinervtisy, it deosn't mttaer in waht
oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist
and lsat ltteer are in the rghit pclae. The rset can be a toatl mses and
you can sitll raed it wouthit a porbelm. Tihs is bcuseae we do not raed
ervey lteter by it slef but the wrod as a wlohe and the biran fguiers it
out aynawy.
... so please excuse us for every typo in the documentation, man pages or
code, btw fixes and patches are welcome.
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==============================================================================
R E Q U I R E D L I B R A R I E S
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MANDATORY:
- libpcap >= 0.8.1
- libnet >= 1.1.2.1
- libpthread
- zlib
OPTIONAL:
To enable plugins:
- libltdl (part of libtool)
To have perl regexp in the filters:
- libpcre
To support SSH and SSL decryption:
- openssl 0.9.7
For the cursed GUI:
- ncurses >= 5.3
For the GTK+ GUI:
- pkgconfig >= 0.15.0
- Glib >= 2.2.2
- Gtk+ >= 2.2.2
- Atk >= 1.2.4
- Pango >= 1.2.3
============================================================================
LICENSE
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GNU GENERAL PUBLIC LICENSE.
see COPYING for details...
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AUTHORS
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Alberto Ornaghi (ALoR) <alor@users.sourceforge.net>
Marco Valleri (NaGA) <naga@antifork.org>
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INSTALLATION
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The easiest way to compile ettercap is in the form:
./configure
make
make install
read INSTALL for further details... and REAME.PLATFORMS for any issue
regarding your operating system.
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HOW TO USE IT
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You can choose between 3 User Interfaces: Text mode, Curses, GTK.
Please read the man pages ettercap(8) and ettercap_curses(8) to learn how
to use ettercap.
============================================================================
TECHNICAL PAPER
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THE HOST LIST
Sending one ARP REQUEST for each ip in the lan (looking at the current ip
and netmask), it is possible to get the ARP REPLIES and than make the
list of the hosts that are responding on the lan. With this method even
windows hosts, reply to the call-for-reply (they don't reply on
broadcast-ping).
Be very careful if the netmask is a class B (255.255.0.0) because ettercap
will send 255*255 = 65025 arp requests (the default delay between two
requests is 1 millisecond, can be configured in etter.conf)
UNIFIED SNIFFING
Ettercap NG uses the unified sniffing method which is the base for all the
attacks. The kernel ip forwarding is always disabled and this task is
accomplished by ettercap itself. Packet that needs to be forwarded are packets
with destination mac address equal to the attacker's one, but with different ip
address. Those packets are re-sent back to the wire to the real destination.
This way, you can plug in variuous mitm attacks at a time. You can even use
external attacker/poisoner, they only have to redirect packets to ettercap's
host and the game is over ;)
BRIDGED SNIFFING
ARP POISONING ATTACK
When you select this method, ettercap will poison the arp cache of the
two hosts, identifying itself as the other host respectively (see the
next section for this).
Once the arp caches are poisoned, the two hosts start the connection, but
their packets will be sent to us, and we will record them and, next,
forward them to the right side of the connection. So the connection is
transparent to the victims, not arguing that they are sniffed. The only
method to discover that there is a man-in-the-middle in your connection, is
to watch at the arp cache and check if there are two hosts with the same
mac address!
That is how we discover if there are others poisoning the arp cache
in our LAN, thus being warned, that our traffic is under control! =)
HOST 1 - - - - - - - - - - - - - - - - - - - -> HOST 2
(poisoned) (poisoned)
| ^
| |
------------> ATTACKER HOST ------------------
( ettercap )
Legenda:
- - - -> the logic connection
-------> the real one
The arp protocol has an intrinsic insecurity. In order to reduce the
traffic on the cable, it will insert an entry in the arp cache even if it
wasn't requested. In other words, EVERY arp reply that goes on the wire
will be inserted in the arp table.
So, we take advantage of this "feature", sending fake arp replies to the two
hosts we will sniff. In this reply we will tell that the mac address of the
second host is the one hard-coded on OUR ethernet card. This host will now
send packets that should go to the first host, to us, because he carries
our mac address.
The same process is done for the first host, in inverse manner, so we have
a perfect man-in-the-middle connection between the two hosts, legally
receiving their packets!!
Example:
HOST 1: mac: 01:01:01:01:01:01 ATTACKER HOST:
ip: 192.168.0.1 mac: 03:03:03:03:03:03
ip: 192.168.0.3
HOST 2: mac: 02:02:02:02:02:02
ip: 192.168.0.2
we send arp replys to:
HOST 1 telling that 192.168.0.2 is on 03:03:03:03:03:03
HOST 2 telling that 192.168.0.1 is on 03:03:03:03:03:03
now they are poisoned !! they will send their packets to us !
then if receive packets from:
HOST 1 we will forward to 02:02:02:02:02:02
HOST 2 we will forward to 01:01:01:01:01:01
simple, isn't it ?
*** LINUX KERNEL 2.4.x ISSUE ***
In the latest release of the linux kernel we can find in :
/usr/src/linux/net/ipv4/arp.c
/* Unsolicited ARP is not accepted by default.
It is possible, that this option should be enabled for some
devices (strip is candidate)
*/
these kernels uses a special neighbor system to prevent unsolicited arp
replies (what ettercap sends to the victim).
Oh shit is ettercap unuseful with that kernel ? the answer is NO !
let's view why... in the same source code we find:
/*
* Process entry. The idea here is we want to send a reply if it is a
* request for us or if it is a request for someone else that we hold
* a proxy for. We want to add an entry to our cache if it is a reply
* to us or if it is a request for our address.
* (The assumption for this last is that if someone is requesting our
* address, they are probably intending to talk to us, so it saves time
* if we cache their address. Their address is also probably not in
* our cache, since ours is not in their cache.)
*
* Putting this another way, we only care about replies if they are to
* us, in which case we add them to the cache. For requests, we care
* about those for us and those for our proxies. We reply to both,
* and in the case of requests for us we add the requester to the arp
* cache.
*/
so, if the kernel receive a REQUEST it will cache the host...
what does that mean ? if ettercap sends spoofed REQUESTS instead of
REPLIES the kernel will cache them ? the answer is YES !!
ettercap 0.6.0 and later has this new ARP REQUEST POISONING method.
it will alternate request and replies on poisoning because other OS doesn't
have this "feature"...
*** SOLARIS ISSUE ***
Solaris will not cache a reply if it isn't already in the cache.
The trick is simple, before poisoning, ettercap sends a spoofed ICMP
ECHO_REQUSET to the host, it has to reply on it and it will make an arp
entry for the spoofed host. Then we can begin to poison as always, the
entry is now in the cache...
ICMP REDIRECTION
This attack implements ICMP redirection. It sends a spoofed icmp redirect
message to the hosts in the lan pretending to be a best route for internet.
All connections to internet will be redirected to the attacker which, in turn,
will forward them to the real gateway. The resulting attack is an HALF-DUPLEX
mitm. Only the client is redirected, since the gateway will not accept redirect
messages for a directly connected network.
DHCP SPOOFING
This attack implements DHCP spoofing. It pretends to be a DHCP server and try
to win the race condition with the real one to force the client to accept
replies from it. This way the attacker is able to manipulate the GW parameter and
hijack all the outgoing traffic generated by the clients.
The resulting attack is an HALF-DUPLEX mitm.
PORT STEALING
This techinque is useful to sniff in a switched environment when ARP poisoning
is not effective (for example where static mapped ARPs are used).
It floods the LAN with ARP packets. The destination MAC address of each
"stealing" packet is the same as the attacker's one (other NICs won't see these
packets), the source MAC address will be one of the MACs of the victims.
This process "steals" the switch's port of each victim.
Using low delays, packets destinated to "stolen" MAC addresses will be received
by the attacker, winning the race condition with the real port owner.
When the attacker receives packets for "stolen" hosts, it stops the flooding
process and performs an ARP request for the real destination of the packet.
When it receives the ARP reply it's sure that the victim has "taken back" his
port, so ettercap can re-send the packet to the destination as is.
Now we can re-start the flooding process waiting for new packets.
CHARACTERS INJECTION
We have stated that the packets are for us...
And the packets will not be received by destination until we forward them.
But what happens if we change them?
Yes, they reach destination with our modifications.
We can modify, add, delete the content of these packets, by simply
recalculating the checksum and substituting them on the traffic.
But we can do also more: we can insert packets in the connection.
We forge our packets with the right sequence and acknowledgement number and
send them to the desired host. When the next packets will pass through us
we simply subtract or add the sequence number with the amount of data we
have injected till the connection is alive, preventing the connection to be
rejected (this until we close ettercap, who maintains sequence numbers
correct, after program exit, the connection must be RESET or all future
traffic would be rejected, blocking the source workstation network).
NOTE: Injector supports escape sequences. you can make multi-line injection
eg: "this on line one \n this on line two \n and so on..."
eg: "this in hex mode: \x65\x6c\x6c\x65"
eg: "this in oct mode: \101\108\108\101"
NOTE: remember to terminate your injection with \r\n if you want to inject
command to the server.
SSH1 MAN-IN-THE-MIDDLE
When the connection starts (remember that we are the master-of-packets, all
packets go through ettercap) we substitute the server public key with one
generated on the fly and save it in a list so we can remember that this
server has been poisoned before.
Then the client send the packet containing the session key ciphered with
our key, so we are able to decipher it and sniff the real 3DES session key.
Now we encrypt the packet with the correct server public key and forward it
to the SSH daemon.
The connection is established normally, but we have the session key !!
Now we can decrypt all the traffic and sit down watching the stream !
The connection will remain active even if we exit from ettercap, because
ettercap doesn't proxy it (like dsniff). After the exchange of the keys,
ettercap is only a spectator... ;)
PACKET FILTERING
Like character injection, we can modify the packets payload and replace
the right sequence and acknowledgement number if needed.
With the integrated filtering engine you can program your own filters
to make the best filter for your aims.
A scripting languages is used to make filters source that must be compiled
with etterfilter(8) in order to be used by ettercap.
PASSIVE SCANNING OF THE LAN
This feature is very useful if you want to know the topology of the lan but
you don't want to send any packet on it. In this way the scan is done entirely
by sniffing packets and extracting useful information from them.
This scan will let you know the hosts in the lan (it watches ARP request), the
Operating System of the hosts (it uses passive os fingerprint... see next
section), the open ports of an host (looking the syn+ack packet), the gateway,
the routers or hosts atcing as a router (it watches ICMP messages).
As a passive method it is useless on a switched lan (because it can make a
topology only of the host that are conneting to you), but if you put it on a
gateway and let it run for hours or days, it will make a complete report of
the hosts in the lan.
PASSIVE OS FINGERPRINT
The main idea is to analyze the passive information coming form an host
when it makes or receives connections with other hosts. This information
is enough to detect the OS and the running services of the host.
In this scenario, we look at SYN and SYN+ACK packet and collect some
interesting info from them:
Window Size: the TCP header field
MSS: the TCP option Maximum Segment Size (can be present or not)
TTL: the IP header field Time To Live (rounded to the next power of 2)
Window Scale: the TCP option indicating the Scale
SACK: the TCP option for the Selective ACK
NOP: if the TCP options contain a NOP
DF: the IP header field Don't Fragment
TIMESTAMP: if the TCP timestamp option is enabled
and obviously the type of the packet (syn or syn+ack)
The database contains different fingerprints for each type of packet
because some OSes have different fingerprints from SYN to SYN+ACK.
Obviously the SYN fingerprint is more reliable, because the SYN+ACK is
influenced by the SYN (if a SYN doen't contain a SACK the SYN+ACK will not
have the SACK option even if the host support it). So while collecting
information off the lan, if we receive a SYN+ACK we mark the OS of that
host as temporary and when we receive a SYN we confirm that.
Fingerprint ending with an ":A" are less reliable... this is the reason
because some OS identification may change during the gathering process.
The SYN+ACK packets are used also to discover the open ports of an host.
(see next section)
The intersting thing is that firewalls, gateways and NAT are trasparent to
passive OS detection. So colleting info for the LAN will let you know info
even for remote host. Only proxies aren't trasparent because they make a
new connection to the target.
Our fingerprint database has to be enlarged, so if you find a host with an
unknown fingerprint and you know for sure the OS of that host, please mail
us <alor@users.sourceforge.net> the fingerpring and the OS, we will insert
in the database.
OPEN PORTS
Open ports are identified by looking for stn+ack packets.
If a syn+ack comes form a port, it is for sure open, except for the
channel command of FTP protocol, for that reason syn+ack going to port 20
are not used to indicate a open port.
For the udp ports the question is a little bit difficult because no syn or
ack packet are present in the udp protocol, so ettercap assumes that a udp
port < 1024 that sends packets is opened. We know that in this way we cannot
discover open ports > 1024 but they can be misdetected as open when a client
sends packet to a server.
GATEWAY AND ROUTERS
The gateway is simply recognized looking at IP packet with a non local ip
( checking the netmask ). If a non local IP is found, ettercap look at the
ethernet address (MAC) and store it as the gateway mac address, then it
search for it in the list and mark the corresponding ip as the gateway.
Looking in the ICMP messages we can rely that if a host sends a
TTL-exceeded or a redirect messages it is a router or an host acting as it.
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