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Man Pages


Manual Reference Pages  -  RWSCAN (1)

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NAME

rwscan - Detect scanning activity in a SiLK dataset

CONTENTS

SYNOPSIS



  rwscan [--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



DESCRIPTION

rwscan 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:
o the ratio of flows with no ACK bit set to all flows
o the ratio of flows with fewer than three packets to all flows
o the average number of source ports per destination IP address
o the ratio of the number of flows that have an average of 60 bytes/packet or greater to all flows
o the ratio of the number of unique destination IP addresses to the total number of flows
o 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:
o the ratio of flows with fewer than three packets to all flows
o the maximum run length of IP addresses per /24 subnet
o the maximum number of unique low-numbered (less than 1024) destination ports contacted on any one host
o the maximum number of consecutive low-numbered destination ports contacted on any one host
o the average number of unique source ports per destination IP address
o the ratio of flows with 60 or more bytes/packet to all flows
o 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:
o the maximum number of consecutive /24 subnets that were contacted
o the maximum run length of IP addresses per /24 subnet
o the maximum number of IP addresses contacted in any one /24 subnet
o the total number of IP addresses contacted
o 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:
o The traffic being analyzed is UDP or ICMP traffic, which rwscan’s implementation of TRW cannot process.
o The TRW model has identified the source as benign. This occurs when the scan probability drops below a configured minimum during sequential hypothesis testing.
o 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.

LIMITATIONS

rwscan 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 ALSO

rwscanquery(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.
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SiLK 3.11.0.1 RWSCAN (1) 2016-04-05

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