Ubuntu Manpage: doscan - Denial Of Service Capable Auditing of Networks

NAME

       doscan - Denial Of Service Capable Auditing of Networks

SYNOPSIS

       doscan options prefix...

DESCRIPTION

       doscan is a tool to discover TCP services ony our network.  It is designed for scanning a single ports on
       a large network.  (There are better tools for scanning many ports on a small set of  hosts,  for  example
       nmap(8).)

       The  prefix  parameter  instructs  doscan  to  scan all addresses in this prefix.  Prefix notation is, as
       usual, A.B.C.D/L, where A.B.C.D is an IP address in dotted-quad notation, and L is a prefix length from 1
       to 32.  If the /L part is omitted, /32 is assumed (and a single host is scanned).

       doscan  uses  a  random  scatter  technology  to  distribute the load across the network.  Within a given
       prefix, hosts are not scanned sequentially, but in  a  random-looking,  but  reproducible  order.   As  a
       result,  doscan  will not stress-test the network edge (just the next hop).  (The prefixes themselves are
       scanned in order.)

OPTIONS

The --port option is mandatory, all other options are optional.

-a timeout, --add-timeout timeout
-A count, --add-burst count
These options specify the timeout (in milliseconds) before new connections are added, and the
number of new connections or hosts to add in one burst. Each timeout millisecond, count new
hosts are contacted. (The per-host timeout controlled by the --timeout option is independent. It
specifies the timeout once the first packet has been sent.)

-b count, --banner count
doscan reads at most count bytes from the remote host. The exact effect of this option varies
among protocol modules, see the PROTOCOL MODULES section for details.

-c count, --connections count
At most count connections are established in parallel. See CAVEATS below for problems resulting
from system file descriptor limits, and instructions for choosing this parameter. By default, at
most 50 parallel connections are established.

-E, --no-epoll
Do not use the epoll kernel interface even if it's available (useful for debugging).

-f, --file name
doscan reads prefixes from the file name, in addition to the command line. The file shall contain
one prefix per line. See the DESCRIPTION section above for the prefix format. To better
distribute scanning of long prefix lists, all prefixies are reorded randomly if the --file option
is used.

-i, --indicator
Display a progress indicator. If doscan is invoked with this option, the number of connections
which have been established so far, the total number of addresses to be scanned, the number of
currently active connections, and the number of hosts for which a report entry has been generated
are displayed periodically.

-n, --net-errors
Instructs doscan to report network errors even if they prevent a connection. Normally, such
errors are suppressed.

-o format, --output format
This option changes the format which doscan uses to report its findings. See the OUTPUT FORMAT
section below for details.

-p port, --port port
The --port option controls to which TCP port doscan connects when scanning a host.

--protocol Istring, -P Istring
Chooses the protocol module string. See the PROTOCOL MODULES section for information on available
protocol modules.

--send string, -s string
--receive regexp, -r regexp
The effects of these options depend on the protocol module. See the PROTOCOL MODULES section for
details.

--style style, -S style
This option controls the output style. See the OUTPUT FORMAT section for details.

-t timeout, --timeout timeout
This option sets the connect timeout to timeout milliseconds. If this time passes without a
successfully established connection, doscan skips the hosts.

-v, --verbose
Turn on additional reporting to standard error.

-h, --help
Display help message and exit.

-V, --version
Output version information and exit.

PROTOCOL MODULES

doscan supports several protocol modules. By default, the generic tcp module is used, but you can choose
another module using the --protocol option. The effect of the --banner, --send and --receive options
depends on the protocol module. Available modules include:

http This module causes doscan to connect to HTTP servers, send a request, and collect the server
identification from the response.

The --banner option specifies the maximum receive buffer size. It defaults to 4000 bytes.

The --send option specifies the request that is send to the server. The string can include C
escape sequences to send control characters. By default, the request GET / HTTP/1.0\r\n\r\n (that
is, GET / HTTP/1.0 followed by the four characters CR, LF, CR, LF) is sent.

The --receive option is not supported by this protocol module.

http_proxy
This protocol module probes hosts for open HTTP proxies. The --port option controls the port that
is probed. The required --receive option must be an integer in the range from 1 to 65534, the
number specifies the port on which doscan listens for the connections from open proxies. The
required --send option specifies the HTTP request method, either "GET" or "CONNECT".

The --banner option is not supported by this protocol module.

Warning: In the worst case, the amount of file descriptors is slightly more than twice the number
of parallel connections given by the --connections options. The additional file descriptors are
used by doscan's HTTP server component to process the connections from open proxies.

See the EXAMPLES section for some convenient combinations of those otions.

ident_check
This protocol module reports hosts which have TCP service listening on the specified port which is
not a proper IDENT/AUTH daemon. It is most useful with a --port 113 command line argument. None
of the --banner, --receive and --send options are supported.

tcp This module is intended for generic TCP service probing and fingerprinting.

The --banner option controls the maximum length of banner strings which are collected. If its
argument is zero or if the option is not specified, no banner strings are collected. In this
case, doscan closes connections immediately after they have been established (which results in an
increased scanning rate).

After establishing a connection, doscans sends the string specified by the --send option to the
remote host. The string can contain the usual C escape sequences (including \000), to send non-
printable characters.

The --receive option specifies a Perl-compatible regular expression (PCRE), and doscan uses it to
analyze the data returned by a remote host. The regular expression may contain at least one
capturing subpattern, it is always anchored at the beginning of the received data. The character .
(period) matches all characters (including newline). $ (dollar sign) matches the very end of the
received data (which may, however, still be incomplete). See pcrepattern(3) for details about the
syntax of Perl-compatible regular expression.

The --receive regular expression is used by doscan for several purposes. If data is received from
a remote host, and if the regular expression ends with $, doscan immediately closes the connection
if all the data received so far from this host matches the regular expression. (doscan assumes
that the reply is complete; increased scanning speed is the result.) When a connection is
terminated for any reason, doscan checks if the regular expression matches the collected data. If
it doesn't, a no match error is recorded (if no other error occured). If it does, and the regular
expression contains a capturing subpattern, that subpattern is recorded. Otherwise, the whole
data is recorded.

In order to use the --receive option, you have to specify the --banner option as well.

udp This module is a generic UDP scanner, as far such a thing is possible. It sends up to five UDP
packets (whose payload is controlled by the mandatory --send option) to the specified port.
Replies are collected. The --banner option is implicit and set to the maximum payload size.
Retransmission is stopped when the first reply is received.

In verbose mode (with both --verbose and --net-errors options), a warning like "stray UDP packet
from 192.0.2.4:7" is printed to standard error when an unexpected UDP packets is received.
Packets to sent to network or broadcast adresses trigger such packets, and poorly implemented UDP
services on multi-homed machines answer with a different source IP address.

OUTPUT FORMAT

doscan prints all gathered data about scanned prefixes to standard output, just before the program
terminates. The output format can be changed with the --output option. The format argument of this
option is a string which includes % substitions, similar to printf(3). The following substitions are
supported

%% A literal percent character.

%a The address of the remote host.

%b The banner return by the host.

%e The error code as a string, empty if no error occurred while scanning the host.

This is either a system error constant (such as ECONNREFUSED), or the string unknown (unknown
error code). If the --receive option is active and the received data does not match the specified
regular expresion, and no other error has occured, the column contains no match.

%E The numeric error code corresponding to the %e error message, or zero if no error occurred.
Negativ error numbers are returned for internal errors (such as a failed match against the
--receive regular expression).

%n The host name corresponding to the scanned IP address (based on a DNS lookup). Note that this
slows down reporting a lot, in general. For this reason, it is not recommended to use %n together
with --style unsorted.

%N A verbatim ASCII LF (newline) character.

%r The time when the information was gathered, measured in seconds since the scanning started.

%t The time when the information was gathered, in local time.

%T Same as %t, but in UTC (also known as GMT).

%% A verbatim percent sign (%).

The default value for the --output option is %T\t%a\t%e\t%b, where \t denotes an ASCII HTAB character.

The --style or -S option supports the following arguments:

sort-by-host
The output is sorted by the IP address of the scanned host. (This is the default.)

unsorted
The output is not sorted and appears in the order the hosts responded.

Caution: Do not use this style together with an --output argument which includes %n, and do not
pipe the output of doscan to a process which cannot read its standard input quickly. Output is
performed synchronously, and if it is delayed, this might impact the scanning activity.

In all cases except unsorted, output is delayed just before the termination of the program.

EXAMPLES

doscan --banner 100 --port 13 192.0.2.1

Prints the time on the host 192.0.2.1 (if it runs a daytime server).

doscan --banner 100 --receive '(.*)\n$' --port 22 192.0.2.0/24

Scan for SSH servers and record the banners (usually containing version information about the SSH
server).

doscan --banner 200 --receive '(.*?)\r?\n$' --port 25 192.0.2.0/24

Scan for SMTP servers and record their greeting messages. Works for FTP as well, with --port 21 instead
of --port 25.

doscan --banner 2000 --send 'GET / HTTP/1.0\r\n\r\n' \
--receive '.*?\nServer: *([^\r\n]*) *\r?\n.*$' \
--port 80 192.0.2.0/24

Scan for HTTP servers and record their version strings.

doscan --protocol http_proxy --port 3128 \
--send GET --receive 80 192.0.2.0/24

Scan for open proxies on TCP port 3128, using the GET HTTP request method. Try to connect back to port
80 on the scanning host.

It is recommended that you use port 80 for the listening port if you scan using GET requests. For
CONNECT requests, port 443 should be used (see below). Some administrators might restrict CONNECT to TCP
port 443 (or filter it for the GET request method), so these choices give best results.

doscan --protocol http_proxy --port 8080 \
--send CONNECT --receive 443 192.0.2.0/24

Scan for open proxies on TCP port 8080, using the CONNECT HTTP request method. Try to connect back to
port 443 on the scanning host.

CAVEATS

The most important option for tuning is --connections. Increasing this option can greatly increase
scanning performance. However, there a two caveats: Many connections require many sockets, and your
system might not support so many of them. Furthermore, a large number of parallel connections generates
significant numbers of packets, and a high CPU load, which can both lead to spurious connection failures
(false negatives).

To increase the number of connections your system can process, you usually have to raise the
corresponding ulimit value in your shell, which requires root privileges. For example, in bash(1), you
can invoke

ulimit -n 10030

to raise the descriptor limit to 10030. You can then pass --connections 10000 to doscan. (Some file
descriptors are not used for scanning, but have to be open nonetheless, and count towards the ulimit -n
limit.)

On Linux-based systems, you might have to adjust some sysctl values which control system-wide descriptor
limits. Refer to sysctl.conf(5), the Documentation directory in the Linux source tree, or the source
code itself for details.

Note, however, that if you increase the number of parallel connections beyond a certain value, you will
lose some hosts, that is they will not be reported even though they are running a service on the scanned
port. Therefore, you should watch both network and CPU utilization to detect bottlenecks. Although the
random scatter technique employed by doscan tries to split the load across your whole network, this
obviously fails if the next hop cannot bear the traffic.

AUTHOR

       doscan was written by Florian Weimer.