DOSCAN(1)DOSCAN(1)NAMEdoscan - Denial Of Service Capable Auditing of Networks
SYNOPSISdoscan options prefix...
DESCRIPTIONdoscan is a tool to discover TCP services on your 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 exam‐
ple 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 sequen‐
tially, 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 connec‐
tion, 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 MODULESdoscan 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 con‐
trol 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 lis‐
tening on the specified port which is not a proper IDENT/AUTH
daemon. It is most useful with a --port 113 command line argu‐
ment. None of the --banner, --receive and --send options are
supported.
tcp This module is intended for generic TCP service probing and fin‐
gerprinting.
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 speci‐
fied 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 expres‐
sion (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 charac‐
ters (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-compati‐
ble 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 subpat‐
tern, 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 FORMATdoscan prints all gathered data about scanned prefixes to standard out‐
put, 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 speci‐
fied regular expresion, and no other error has occured, the col‐
umn 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 argu‐
ment 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 termi‐
nation of the program.
EXAMPLESdoscan--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 nega‐
tives).
To increase the number of connections your system can process, you usu‐
ally 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 --connec‐
tions 10000 to doscan. (Some file descriptors are not used for scan‐
ning, 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.
AUTHORdoscan was written by Florian Weimer.
SEE ALSOnmap(8), pcrepattern(3), sysctl.conf(5) (on GNU/Linux systems), shell
documentation for the ulimit interface
2003-07-27 DOSCAN(1)
