rwscan(1) SiLK Tool Suite rwscan(1)NAMErwscan - Detect scanning activity in a SiLK dataset
SYNOPSISrwscan [--scan-model=MODEL] [--output-path=OUTFILE]
[--trw-internal-set=SETFILE]
[--trw-theta0=PROB] [--trw-theta1=PROB]
[--no-titles] [--no-columns] [--column-separator=CHAR]
[--no-final-delimiter] [{--delimited | --delimited=CHAR}]
[--integer-ips] [--model-fields] [--scandb]
[--threads=THREADS] [--queue-depth=DEPTH]
[--verbose-progress=CIDR] [--verbose-flows]
[ {--verbose-results | --verbose-results=NUM} ]
[--site-config-file=FILENAME]
[FILES...]
rwscan--help
rwscan--version
DESCRIPTIONrwscan reads sorted SiLK Flow records, performs scan detection analysis
on those records, and outputs textual columnar output for the scanning
IP addresses. rwscan writes its out to the --output-path or to the
standard output when --output-path is not specified.
The types of scan detection analysis that rwscan supports are Threshold
Random Walk (TRW) and Bayesian Logistic Regression (BLR). Details
about these techniques are described in the "METHOD OF OPERATION"
section below.
rwscan is designed to write its data into a database. This database
can be queried using the rwscanquery(1) tool. See the "EXAMPLES"
section for the recommended database schema.
The input to rwscan should be pre-sorted using rwsort(1) by the source
IP, protocol, and destination IP (i.e., --fields=sip,proto,dip).
rwscan reads SiLK Flow records from the files named on the command line
or from the standard input when no file names are specified. To read
the standard input in addition to the named files, use "-" or "stdin"
as a file name. If an input file name ends in ".gz", the file will be
uncompressed as it is read.
OPTIONS
Option names may be abbreviated if the abbreviation is unique or is an
exact match for an option. A parameter to an option may be specified
as --arg=param or --arg param, though the first form is required for
options that take optional parameters.
--scan-model=MODEL
Select a specific scan detection model. If not specified, the
default value for MODEL is 0. See the "METHOD OF OPERATION"
section for more details.
0 Use the Threshold Random Walk (TRW) and Bayesian Logistic
Regression (BLR) scan detection models in series.
1 Use only the TRW scan detection model.
2 Use only the BLR scan detection model.
--output-path=OUTFILE
Specify the output file that scan records will be written to. If
not specified, the scan records are written to standard output.
--trw-internal-set=SETFILE
Specify an IPset file containing all valid internal IP addresses.
This parameter is required when using the TRW scan detection model,
since the TRW model requires the list of targeted IPs (i.e., the
IPs to detect the scanning activity to). This switch is ignored
when the TRW model is not used. For information on creating IPset
files, see the rwset(1) and rwsetbuild(1) manual pages. Prior to
SiLK 3.4, this switch was named --trw-sip-set.
--trw-sip-set=SETFILE
This is a deprecated alias for --trw-internal-set.
--trw-theta0=PROB
Set the theta_0 parameter for the TRW scan model to PROB, which
must be a floating point number between 0 and 1. theta_0 is
defined as the probability that a connection succeeds given the
hypothesis that the remote source is benign (not a scanner). The
default value for this option is 0.8. This option should only be
used by experts familiar with the TRW algorithm.
--trw-theta1=PROB
Set the theta_1 parameter for the TRW scan model to PROB, which
must be a floating point number between 0 and 1. theta_1 is
defined as the probability that a connection succeeds given the
hypothesis that the remote source is malicious (a scanner). The
default value for this option is 0.2. This option should only be
used by experts familiar with the TRW algorithm.
--no-titles
Turn off column titles. By default, titles are printed.
--no-columns
Disable fixed-width columnar output.
--column-separator=C
Use specified character between columns. When this switch is not
specified, the default of '|' is used.
--no-final-delimiter
Do not print the column separator after the final column. Normally
a delimiter is printed.
--delimited
--delimited=C
Run as if --no-columns --no-final-delimiter --column-sep=C had been
specified. That is, disable fixed-width column output; if
character C is provided, it is used as the delimiter between
columns instead of the default '|'.
--integer-ips
Print IP addresses as decimal integers instead of in their
canonical representation.
--model-fields
Show scan model detail fields. This switch controls whether
additional informational fields about the scan detection models are
printed.
--scandb
Produce output suitable for loading into a database. Sample
database schema are given below under "EXAMPLES". This option is
equivalent to --no-titles --no-columns --no-final-delimiter
--model-fields --integer-ips.
--threads=THREADS
Specify the number of worker threads to create for scan detection
processing. By default, one thread will be used. Changing this
number to match the number of available CPUs will often yield a
large performance improvement.
--queue-depth=DEPTH
Specify the depth of the work queue. The default is to make the
work queue the same size as the number of worker threads, but this
can be changed. Normally, the default is fine.
--verbose-progress=CIDR
Report progress as rwscan processes input data. The CIDR argument
should be an integer that corresponds to the netblock size of each
line of progress. For example, --verbose-progress=8 would print a
progress message for each /8 network processed.
--verbose-flows
Cause rwscan to print very verbose information for each flow. This
switch is primarily useful for debugging.
--verbose-results
--verbose-results=NUM
Print detailed information on each IP processed by rwscan. If a
NUM argument is provided, only print verbose results for sources
that sent at least NUM flows. This information includes scan model
calculations, overall scan scores, etc. This option will generate
a lot of output, and is primarily useful for debugging.
--site-config-file=FILENAME
Read the SiLK site configuration from the named file FILENAME.
When this switch is not provided, rwscan searches for the site
configuration file in the locations specified in the "FILES"
section.
--help
Print the available options and exit.
--version
Print the version number and information about how SiLK was
configured, then exit the application.
METHOD OF OPERATION
rwscan's default behavior is to consult two scan detection models to
determine whether a source is a scanner. The primary model used is the
Threshold Random Walk (TRW) model. The TRW algorithm takes advantage
of the tendency of scanners to attempt to contact a large number of IPs
that do not exist on the target network.
By keeping track of the number of "hits" (successful connections) and
"misses" (attempts to connect to IP addresses that are not active on
the target network), scanners can be detected quickly and with a high
degree of accuracy. Sequential hypothesis testing is used to analyze
the probability that a source is a scanner as each flow record is
processed. Once the scan probability exceeds a configured maximum, the
source is flagged as a scanner, and no further analysis of traffic from
that host is necessary.
The TRW model is not 100% accurate, however, and only finds scans in
TCP flow data. In the case where the TRW model is inconclusive, a
secondary model called BLR is invoked. BLR stands for "Bayesian
Logistic Regression." Unlike TRW, the BLR approach must analyze all
traffic from a given source IP to determine whether that IP is a
scanner.
Because of this, BLR operates much slower than TRW. However, the BLR
model has been shown to detect scans that are not detected by the TRW
model, particularly scans in UDP and ICMP data, and vertical TCP scans
which focus on finding services on a single host. It does this by
calculating metrics from the flow data from each source, and using
those metrics to arrive at an overall likelihood that the flow data
represents scanning activity.
The metrics BLR uses for detecting scans in TCP flow data are:
· the ratio of flows with no ACK bit set to all flows
· the ratio of flows with fewer than three packets to all flows
· the average number of source ports per destination IP address
· the ratio of the number of flows that have an average of 60
bytes/packet or greater to all flows
· the ratio of the number of unique destination IP addresses to the
total number of flows
· the ratio of the number of flows where the flag combination
indicates backscatter to all flows
The metrics BLR uses for detecting scans in UDP flow data are:
· the ratio of flows with fewer than three packets to all flows
· the maximum run length of IP addresses per /24 subnet
· the maximum number of unique low-numbered (less than 1024)
destination ports contacted on any one host
· the maximum number of consecutive low-numbered destination ports
contacted on any one host
· the average number of unique source ports per destination IP
address
· the ratio of flows with 60 or more bytes/packet to all flows
· the ratio of unique source ports (both low and high) to the number
of flows
The metrics BLR uses for detecting scans in ICMP flow data are:
· the maximum number of consecutive /24 subnets that were contacted
· the maximum run length of IP addresses per /24 subnet
· the maximum number of IP addresses contacted in any one /24 subnet
· the total number of IP addresses contacted
· the ratio of ICMP echo requests to all ICMP flows
Because the TRW model has a lower false positive rate than the BLR
model, any source identified as a scanner by TRW will be identified as
a scanner by the hybrid model without consulting BLR. BLR is only
invoked in the following cases:
· The traffic being analyzed is UDP or ICMP traffic, which rwscan's
implementation of TRW cannot process.
· The TRW model has identified the source as benign. This occurs
when the scan probability drops below a configured minimum during
sequential hypothesis testing.
· The TRW model has identified the source as unknown (where the scan
probability never exceeded the minimum or maximum thresholds during
sequential hypothesis testing).
In situations where the use of one model is preferred, the other model
can be disabled using the --scan-model switch. This may have an impact
on the performance and/or accuracy of the system.
LIMITATIONSrwscan detects scans in IPv4 flows only.
EXAMPLES
In the following examples, the dollar sign ("$") represents the shell
prompt. The text after the dollar sign represents the command line.
Lines have been wrapped for improved readability, and the back slash
("\") is used to indicate a wrapped line.
Basic Usage
Assuming a properly sorted SiLK Flow file as input, the basic usage for
Bayesian Logistic Regression (BLR) scan detection requires only the
input file, data.rw, and output file, scans.txt, arguments.
$ rwscan --scan-model=2 --output-path=scans.txt data.rw
Basic usage of Threshold Random Walk (TRW) scan detection requires the
IP addresses of the targeted network (i.e., the internal IP space),
specified in the internal.set IPset file.
$ rwscan --trw-internal-set=internal.set --output-path=scans.txt data.rw
Typical Usage
More commonly, an analyst uses rwfilter(1) to query the data repository
for flow records within a time window. First, the analyst has rwset(1)
put the source addresses of outgoing flow records into an IPset,
resulting in the IPset containing the IPs of active hosts on the
internal network. Next, the incoming traffic is piped to rwsort(1) and
then to rwscan.
$ rwfilter --start=2004/12/29:00 --type=out,outweb --all-dest=stdout \
| rwset --sip=internal.set
$ rwfilter --start=2004/12/29:00 --type=in,inweb --all-dest=stdout \
| rwsort --fields=sip,proto,dip \
| rwscan --trw-internal-set=internal.set --scan-model=0 \
--output-path=scans.txt
Storing Scans in a PostgreSQL Database
Instead of having the analyst run rwscan directly, often the output
from rwscan is put into a database where it can be queried by
rwscanquery(1). The output produced by the --scandb switch is suitable
for loading into a database of scans. The process for using the
PostgreSQL database is described in this section.
Schemas for Oracle, MySQL, and SQLite are provided below, but the
details to create users with the proper rolls are not included.
Here is the schema for PostgreSQL:
CREATE DATABASE scans
CREATE SCHEMA scans
CREATE SEQUENCE scans_id_seq
CREATE TABLE scans (
id BIGINT NOT NULL DEFAULT nextval('scans_id_seq'),
sip BIGINT NOT NULL,
proto SMALLINT NOT NULL,
stime TIMESTAMP without time zone NOT NULL,
etime TIMESTAMP without time zone NOT NULL,
flows BIGINT NOT NULL,
packets BIGINT NOT NULL,
bytes BIGINT NOT NULL,
scan_model INTEGER NOT NULL,
scan_prob FLOAT NOT NULL,
PRIMARY KEY (id)
)
CREATE INDEX scans_stime_idx ON scans (stime)
CREATE INDEX scans_etime_idx ON scans (etime)
;
A database user should be created for the purposes of populating the
scan database, e.g.:
CREATE USER rwscan WITH PASSWORD 'secret';
GRANT ALL PRIVILEGES ON DATABASE scans TO rwscan;
Additionally, a user with read-only access should be created for use by
the rwscanquery tool:
CREATE USER rwscanquery WITH PASSWORD 'secret';
GRANT SELECT ON DATABASE scans TO rwscanquery;
To import rwscan's --scandb output into a PostgreSQL database, use a
command similar to the following:
$ cat /tmp/scans.import.txt \
| psql -c \
"COPY scans \
(sip, proto, stime, etime, \
flows, packets, bytes, \
scan_model, scan_prob) \
FROM stdin DELIMITER as '|'" scans
Sample Schema for Oracle
CREATE TABLE scans (
id integer unsigned not null unique,
sip integer unsigned not null,
proto tinyint unsigned not null,
stime datetime not null,
etime datetime not null,
flows integer unsigned not null,
packets integer unsigned not null,
bytes integer unsigned not null,
scan_model integer unsigned not null,
scan_prob float unsigned not null,
primary key (id)
);
Sample Schema for MySQL
CREATE TABLE scans (
id integer unsigned not null auto_increment,
sip integer unsigned not null,
proto tinyint unsigned not null,
stime datetime not null,
etime datetime not null,
flows integer unsigned not null,
packets integer unsigned not null,
bytes integer unsigned not null,
scan_model integer unsigned not null,
scan_prob float unsigned not null,
primary key (id),
INDEX (stime),
INDEX (etime)
) TYPE=InnoDB;
Sample Schema and Import Command for SQLite
CREATE TABLE scans (
id INTEGER PRIMARY KEY AUTOINCREMENT,
sip INTEGER NOT NULL,
proto SMALLINT NOT NULL,
stime TIMESTAMP NOT NULL,
etime TIMESTAMP NOT NULL,
flows INTEGER NOT NULL,
packets INTEGER NOT NULL,
bytes INTEGER NOT NULL,
scan_model INTEGER NOT NULL,
scan_prob FLOAT NOT NULL
);
CREATE INDEX scans_stime_idx ON scans (stime);
CREATE INDEX scans_etime_idx ON scans (etime);
To import rwscan's --scandb output into a SQLite database, use the
following command:
$ perl -nwe 'chomp;
print "INSERT INTO scans VALUES (NULL,",
(join ",",map { / / ? qq("$_") : $_ } split /\|/),
");\n";' \
scans.txt | sqlite3 scans.sqlite
ENVIRONMENT
SILK_CLOBBER
The SiLK tools normally refuse to overwrite existing files.
Setting SILK_CLOBBER to a non-empty value removes this restriction.
SILK_CONFIG_FILE
This environment variable is used as the value for the
--site-config-file when that switch is not provided.
SILK_DATA_ROOTDIR
This environment variable specifies the root directory of data
repository. As described in the "FILES" section, rwscan may use
this environment variable when searching for the SiLK site
configuration file.
SILK_PATH
This environment variable gives the root of the install tree. When
searching for configuration files, rwscan may use this environment
variable. See the "FILES" section for details.
FILES
${SILK_CONFIG_FILE}
${SILK_DATA_ROOTDIR}/silk.conf
/data/silk.conf
${SILK_PATH}/share/silk/silk.conf
${SILK_PATH}/share/silk.conf
/usr/local/share/silk/silk.conf
/usr/local/share/silk.conf
Possible locations for the SiLK site configuration file which are
checked when the --site-config-file switch is not provided.
SEE ALSOrwscanquery(1), rwfilter(1), rwsort(1), rwset(1), rwsetbuild(1),
silk(7)BUGS
When used in an IPv6 environment, rwscan converts IPv6 flow records
that contain addresses in the ::ffff:0:0/96 prefix to IPv4. IPv6
records outside of that prefix are silently ignored.
SiLK 3.11.0.1 2016-02-19 rwscan(1)
