FTester(8)FTester(8)NAME
FTester - Firewall and IDS testing tool
SYNOPSIS
ftest [ -c sourceip:sourceport:destip:destport:flags:protocol:tos ] [
-e evasion_method ] [ -d delay ] [ -f file ] [ -F ] [ -g fragments_num‐
ber|fragments_size ] [ -k cksum ] [ -p segments_number|segments_size ]
[ -r ] [ -s time ] [ -t ttl ] [ -m marker ] [ -v ]
ftestd [ -c ttl1:ttl2 ] [ -g ] [ -i interface ] [ -m marker ] [ -v ]
freport ftest.log ftestd.log
DESCRIPTION
FTester is a tool designed for testing firewalls filtering policies and
Intrusion Detection System (IDS) capabilities.
The tool consists of two perl scripts, a packet injector (ftest) and
the listening sniffer (ftestd). The first script injects custom pack‐
ets, defined in ftest.conf , with a signature in the data part while
the sniffer listens for such marked packets. The scripts both write a
log file which is in the same form for both scripts. A 'diff -b' of the
two produced files (ftest.log and ftestd.log) shows the packets that
were unable to reach the sniffer due to filtering rules if these two
scripts are ran on hosts placed on two different sides of a firewall.
Stateful inspection firewalls are handled with the 'connection spoof‐
ing' option. A script called freport is also available for automati‐
cally parse the log files.
Of course this is not an automated process, ftest.conf must be crafted
for every different situation. Examples and rules are included in the
sample configuration file.
The IDS (Intrusion Detection System) testing feature can be used either
with ftest only or with the additional support of ftestd for handling
stateful inspection IDS, ftest can also use common IDS evasion tech‐
niques. Instead of using the configuration syntax the script can also
process snort rule definition file.
OPTIONS
ftest:
-c sourceip:sourceport:destip:destport:flags:protocol:tos
Injects a single packet (override -f option).
-d delay (es. 0.25 = 250 ms)
Delay in milliseconds between each packet injection.
-e evasion_method
See the IDS EVASION section.
-f file
Read configuration from file.
-F When in connection spoofing mode terminate (FIN handshake) the
created connection, useful if you don't want to flood firewall's
connection tracking table with established entries, requires
ftestd reply (see -s flag).
-g fragments_number|fragments_size
Split TCP and UDP marked packets in the specified number of IP
fragments, useful for checking firewall's fragmentation handling
and IDS's fragmentation reassembly. In 'connection spoofing' or
'evasion' mode only packets specified in configuration are frag‐
mented and not connection control ones. Obviously 'frag‐
ments_number' must be >= 2. If the specified number of fragments
is incompatible with payload length ftest will automatically set
the nearest right value.
Additionaly you can specify the fragments size in bytes if you
append the suffix 'b' to the value (es. -g 16b), fragments size
must be a multiple of 8. If the specified fragment's size is
incompatible with payload lenght ftest will automatically set
the nearest right value.
-k checksum
Set a custom checksum instead of the right one when sending
packets, useful to detect if the firewall is blocking invalid
packets.
-p segments_number|segments_size
Specify the number of TCP segments when splitting the tcp stream
in evasion mode, see IDS EVASION for details. If the specified
number of segments is incompatible with payload length ftest
will automatically set the nearest right value.
Additionaly you can specify the segments size in bytes if you
append the suffix 'b' to the value (es. -p 16b). If the speci‐
fied segments's size is incompatible with payload lenght ftest
will automatically set the nearest right value.
If not specified ftest will use the default value of 2 segments.
-r When in connection spoofing mode reset (RST packet) the created
connection, useful if you don't want to flood firewall's connec‐
tion tracking table with established entries, requires ftestd
reply (see -s flag).
-s time
Sleep time in seconds for waiting connection spoofing replies,
see 'connection spoofing' option.
-t ttl Time to live that makes the ttl1/ttl2 evasion option packets
visible to the IDS but not to the target host.
-m marker
Custom marker string that is appended to the standard signature
in generated packets and logs' filenames. Using this option per‐
mits multiple instances of ftest/ftestd to run simultaneously
without interfering with each other.
-v Prints to stdout injected packets and be verbose.
ftestd:
-c ttl1:ttl2
Define TTL settings for the 'connection spoofing' option: set
default stack TTL executing `echo "ttl1" >
/proc/sys/net/ipv4/ip_default_ttl` (Linux only) and set ftestd
reply TTL to ttl2.
-g Enable fragments reassembly when sniffing packets, useful if you
are using ftest fragmentation option and your firewall is not
performing fragments reassembly.
-i interface
Listen on interface, if not specified will default to the first
configured one (excluding loopback).
-m marker
Custom marker string that is tested for in received packets.
Using this option permits multiple instances of ftest/ftestd to
run simultaneously without interfering with each other.
-v Prints to stdout sniffed packets and be verbose.
CONFIGURATION FILE
A - flags
Command line flags can be overrided with the 'flags:' directive at any
point and any time, original flags can be restored with 'flags:
restore'. See the man page or `ftest -h` for available flags.
Examples:
flags: -d 0.01 -s 1
flags: -e ttl1 -p 4
flags: restore
1 - basic form
The main configuration file defines which packets ftest will send to
ftestd, the basic syntax is the following:
Source Address:Source Port:Destination Address:Destination
Port:Flags:Protocol:Type of Service
for TCP and UDP packets
Source Address:Source Port:Destination Address:Destination
Port:Flags:ICMP:icmp_type:icmp_code
for ICMP packets
The Source Address can be specified as a single IP address, a range of
addresses, or a CIDR block.
Source Port and Destination Port can also be specified in ranges.
Valid Flags are A (ACK), F (FIN), P (PUSH), R (RST), S (SYN), U (URG).
Destination Address must be the host where ftestd is sniffing or one
which traffic can be sniffed.
Line beginning with a # are comments and ignored by ftest.
Examples:
192.168.22.3:1025:10.7.0.1:80:AP:TCP:0
192.168.22.3:1025:10.7.0.1:21:A:TCP:0
192.168.22.3:20:10.7.0.1:1025:AP:TCP:10
192.168.22.3:53:10.7.0.1:53::UDP:0
192.168.22.3:1025:10.7.0.1:80::ICMP:3:5
192.168.0.1-255:1024:10.7.0.1:22:S:TCP:0
192.168.0.1:1-1024:10.7.0.1:20-25:S:TCP:22
192.168.0.23:666:10.7.0.1:1-65535:A:TCP:0
192.168.3.0/24:1024:10.7.0.1:22:S:TCP:0
192.168.3.128/25:1-1024:10.7.0.1:20-25:S:TCP:22
192.168.0.0/22:666:10.7.0.1:1-65535:A:TCP:0
2 - connection spoofing
ftest and ftestd are capable of simulating a real connection, this is
extremly useful when you are dealing with a stateful detection firewall
(like netfilter) that blocks packets unrelated to an ongoing connec‐
tion. In such cases packets like 192.168.22.3:1025:10.7.0.1:80:AP:TCP:0
are likely to be blocked by the firewall if their sequence numbers and
flags aren't syncronised with a previously started connection. In
order to circumvent this problem if the packets are specified with the
'connect=' prefix ftest and ftestd will act in this way:
a) ftest will send 192.168.22.3:1025:10.7.0.1:80:S:TCP:0 with a custom
payload and sequence
number set to $random_1, the payload size is 8 byte. Then it sleeps
for a custom time waiting
for the firewall to see the packet specified in b).
b) ftestd will recognize this packet and will send
10.7.0.1:80:192.168.22.3:1025 with
sequence number $random_2+1024 and acknowledge number ($ran‐
dom_1+payload_size+1).
c) ftest, after the sleep period, will complete the connection hand‐
shake sending
192.168.22.3:1025:10.7.0.1:80:A:TCP:0 with sequence number $ran‐
dom_1+payload_size+1 and
acknowledge number $random_2+1024+1
d) ftest will finally send the specified packet with sequence number
$random_1+payload+size+1 and
acknowledge number $random_2+1024+1
e) ftestd acknowledge packet d)
now there is one great problem with this approach, the stack of the
destination host will reply to the packet sent in a) and the real host
we've spoofed will reply to it resetting the connection. So we have to
do two things, hiding the stack response to the spoofed host and to the
firewall and make sure that ftestd reply will traverse the firewall by
not reaching the spoofed host. Hiding the stack response could be done
by setting a very low default TTL in /proc/sys/net/ipv4/ip_default_ttl
(Linux only). Hiding to the spoofed host our reply ( b) ) is done by
setting its TTL to a low value equal to the hop delay between ftestd
and the firewall. For example use ./ftestd -c 0:3 for temporarly set‐
ting default stack ttl to 0 and ftestd reply ttl to 3, the
ip_default_ttl will be restored when a stop_signal is received.
WARNING: if you interrupt ftestd execution and a stop_signal is not
sniffed your default ttl will remain low! Manually restore the default
value with 'echo 64 > /proc/sys/net/ipv4/ip_default_ttl'.
NOTE: you can avoid this ttl mess by firewalling the input chain of the
host or using a unallocated IP address published with a spoofed arp
response.
Remember to specify different sport-dport pairs if you use this mode
again with the same saddr-daddr and you're not using the -r/-F flag.
Use the -s flag for setting the sleep time duration.
Packets a),b),c),e) are NOT logged.
Examples:
connect=192.168.0.1:1025:10.7.0.1:22:AP:TCP:0
connect=192.168.0.1-255:1025-2000:10.7.0.1:53:AP:TCP:0
connect=192.168.0.0/24:1025:10.7.0.1:1-1024:AP:TCP:0
3 - stop signal
The stop signal tells ftestd to close the log file and die, obviously
you must ensure that this packet will reach the sniffer.
Examples:
stop_signal=192.168.0.1:666:10.7.0.1:666:S:TCP:0
4 - IDS testing
ftest has an additional syntax, useful for test Intrusion Detection
System, that permits the definition of the payload. The support of
ftestd is not necessary in this mode since mainly you have to check
your IDS logs, however there is an "ids-conn" option that works just
like the "connect" option, useful if your IDS is performing stateful
inspection.
See also the IDS EVASION section.
Examples:
ids=192.168.0.1:1025:10.7.0.1:25:S:TCP:0:VRFY
ids=192.168.0.1::10.7.0.1:::ICMP:8:0:+++ath
ids-conn=192.168.0.1:23:10.7.0.1:1025:PA:TCP:0:to su root
ids-conn=192.168.0.1:1025:10.7.0.1:80:PA:TCP:0:cmd.exe
ids-conn=192.168.0.1:1026:10.7.0.1:80:PA:TCP:0:ftp.exe
In addition you can use the following syntax to directly use a snort
(http://www.snort.org) rule definition file. The "insert-conn" option
make ftest work as in the "connection spoofing" mode for packets with
flags different than SYN. Source, destination IP and ToS must be speci‐
fied.
The following keywords are currently supported:
content - flags - offset - dsize
source and destination port are randomly selected if specified as
'any', in the case that a sport-dport pair is incidentally repeated
connection spoofing mode won't work unless you're using the -r/-F flag.
Examples:
insert /etc/snort/exploit.rules 192.168.0.1 10.7.0.1 0
insert-conn /etc/snort/exploit.rules 192.168.0.1 10.7.0.1 0
IDS EVASION
A number of IDS evasion techniques are implemented, you can activate
them with the -e flag when using 'ids-conn' and 'insert-conn' modes.
TCP splitting can be controlled with the -p flag (see OPTIONS).
-e stream
packet => [packet1(ATT) + packet2(ACK)]
Simple splitting of the tcp stream
-e stream1
packet => [packet1(ATT) + packet(GARBAGE) [invalid checksum] +
packet2(ACK)]
The IDS will see 'ATTGARBAGEACK' instead of 'ATTACK' if it's not
performing checksum analysis
-e ttl1
packet => [packet1(ATT) [ttl n] + packet(GARBAGE) [ttl p] +
packet2(ATT) [ttl n]]
The IDS will see 'ATTGARBAGEACK' if p is a TTL sufficient to
reach the IDS but not the target host. The ttl can be specified
with the -t flag (see OPTIONS)
-e rst1
packet => [packet1(ATT) + rst [invalid checksum] + packet2(ACK)]
If the IDS is performing a poor connection tracking and it's not
performing checksum analysis it will close the connection ignor‐
ing subsequent packets
-e rst2
packet => [packet1(ATT) [ttl n] + rst [ttl p] + packet2(ACK)
[ttl n]]
The IDS will close the connection if p is a TTL sufficient to
reach the IDS but not the target host. The ttl can be specified
with the -t flag (see OPTIONS)
-e desync1
packet => [packet1(ATT) + syn [wrong ack] + packet2(ACK)]
If the IDS is performing a poor connection tracking it will
resynchronize the connection against the wrong sequence numbers
of the post-connection SYN
-e desync2
packet => [syn [wrong ack+invalid checksum] + syn + packet1(ATT)
+ packet2(ACK)]
If the IDS is performing connection tracking with no checksum
analysis it will synchronize the connection against the wrong
sequence numbers of the pre-connection SYN
-e frag1
packet => [fragment3(C) + fragment2(TA) + fragment1(AT) + frag‐
ment4(K)]
If the IDS can't correctly handle out of order IP fragments it
won't reassemble the packet
-e frag2
packet => [fragment4(K) + fragment3(C) + fragment2(TA) + frag‐
ment1(AT)]
Like frag1 but send the last fragment first
-e frag3
packet => [fragment1(AT) + fragment2(TA) + fragment3(C) + frag‐
ment3(C) + fragment4(K)]
Duplicate the penultimate fragment
-e frag4
packet => [fragment1(AT) + fragment1(OO) + fragment3(TACK)]
Duplicate the first fragment with garbage data. Overlap attack
effective if the IDS favors new data and the host favors old
data.
-e frag5
packet => [fragment1(OO) + fragment1(AT) + fragment3(TACK)]
Send the first fragment with garbage data then duplicate it with
correct payload. Overlap attack effective if the IDS favors old
data and the host favors new data.
A detailed explanation can be find in the following documents:
Phrack Magazine, Volume 8, Issue 54 Dec 25th, 1998, article 10
(P54-10)
Insertion, Evasion, and Denial of Service: Eluding Network
Intrusion Detection - Thomas H. Ptacek, Timothy N.Newsham.
(http://www.nai.com/media/ps/nai_labs/ids.ps)
FILES
ftest.conf
Main configuration file.
ftest.log
Log file generated by ftest.
ftestd.log
Log file generated by ftestd.
EXAMPLES
See the included ftest.conf.
REQUIREMENTS
Net::RawIP, Net::PcapUtils, NetPacket are required, you can grab them
at www.cpan.org or using your CPAN shell (`perl -e shell -MCPAN`).
BUGS
Snort rules parsing is far from perfect, multiple content rules won't
work and non-content rules are skipped as well as ip only ones. Addi‐
tionally variables such as $HTTP_PORTS are currently not recognized and
will create problems (fix is coming soon, in the meantime sed is your
friend ;) ).
ftestd -c flag works only on Linux.
Please report any bugs you find to <andrea@inversepath.com>
TODO
- add an option for sending fragments with splitted TCP/UDP header
- add a OSSTMM (http://www.isecom.org/projects/osstmm.htm) compliant
configuration template (in progress)
- implement other evasion techniques (suggestions?)
- throughput test and report
- improve snort conf parsing
- make ftestd -c flag compatible with other platforms
- perl-tk graphic frontend (in progress)
- use warnings
Any volounteers ? ;)
LICENSE
The FTester is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License version 2 as pub‐
lished by the Free Software Foundation.
AUTHOR
Andrea Barisani <andrea@inversepath.com>
The latest version of FTester can be found at
http://dev.inversepath.com/trac/ftester
NOTES
The IDS testing option that injects packets reading snort configuration
files is designed to test the IDS engine and NOT it's efficiency in
detecting real world attacks, the detection of an attack involve multi‐
ple events and often human intervention to do proper correlation. The
ftester can only be useful to verify things like the IDS placement,
stateful inspection, fragmention handling, overall speed and so on.
Keep this in mind when using this tool.
SEE ALSO
A very similiar tool is the filterrules package, you can find it at
http://www.hsc.fr/ressources/outils/filterrules/index.html.en
Another snort false positive generator is sneeze , you can find it at
http://snort.sourceforge.net/sneeze-1.0.tar
Fragrouter, http://www.anzen.com/research/nidsbench
Fragroute, http://www.monkey.org/~dugsong/fragroute
Stevens, W.Richard. TCP/IP Illustrated, Volume One: The Protocols.
Reading, MA: Addison-Wesley. 1994.
version 1.0 13 Feb 2006 FTester(8)
