8.44. Datasets

Using the dataset and datarep keyword it is possible to match on large amounts of data against any sticky buffer.

For example, to match against a DNS black list called dns-bl:

dns.query; dataset:isset,dns-bl;

These keywords are aware of transforms. So to look up a DNS query against a MD5 black list:

dns.query; to_md5; dataset:isset,dns-bl;

8.44.1. Global config (optional)

Datasets can optionally be defined in the main config. Sets can also be declared from the rule syntax.

Example of sets for tracking unique values:

datasets:
  ua-seen:
    type: string
    state: ua-seen.lst
  dns-sha256-seen:
    type: sha256
    state: dns-sha256-seen.lst

Rules to go with the above:

alert dns any any -> any any (msg:"dns list test"; dns.query; to_sha256; dataset:isset,dns-sha256-seen; sid:123; rev:1;)

alert http any any -> any any (msg: "http user-agent test"; http.user_agent; dataset:set,ua-seen; sid:234; rev:1;)

It is also possible to optionally define global default memcap and hashsize.

Example:

datasets:
  defaults:
    memcap: 100mb
    hashsize: 2048
  ua-seen:
    type: string
    load: ua-seen.lst

or define memcap and hashsize per dataset.

Example:

datasets:
  ua-seen:
    type: string
    load: ua-seen.lst
    memcap: 10mb
    hashsize: 1024

Note

The hashsize should be close to the amount of entries in the dataset to avoid collisions. If it's set too low, this could result in rather long startup time.

8.44.2. Rule keywords

8.44.2.1. dataset

Datasets are binary: something is in the set or it's not.

Syntax:

dataset:<cmd>,<name>,<options>;

dataset:<set|isset|isnotset>,<name> \
    [, type <string|md5|sha256|ipv4|ip>, save <file name>, load <file name>, state <file name>, memcap <size>, hashsize <size>];
type <type>

the data type: string, md5, sha256, ipv4, ip

load <file name>

file name for load the data when Suricata starts up

state

sets file name for loading and saving a dataset

save <file name>

advanced option to set the file name for saving the in-memory data when Suricata exits.

memcap <size>

maximum memory limit for the respective dataset

hashsize <size>

allowed size of the hash for the respective dataset

Note

'type' is mandatory and needs to be set.

Note

'load' and 'state' or 'save' and 'state' cannot be mixed.

Example rules could look like:

  1. Detect unique User-Agents:

alert http any any -> any any (msg:"LOCAL HTTP new UA"; http.user_agent; dataset:set,http-ua-seen, type string, state http-ua-seen.csv; sid:8000001; rev:1;)

  1. Detect unique TLDs:

alert dns $HOME_NET any -> any any (msg:"LOCAL DNS unique TLD"; dns.query; pcrexform:"\.([^\.]+)$"; dataset:set,dns-tld-seen, type string, state dns-tld-seen.csv; sid:8000002; rev:1;)

Following image is a pictorial representation of how the pcrexform works on domain names to find TLDs in the dataset dns-tld-seen:

../_images/detect-unique-tlds.png

Notice how it is not possible to do certain operations alone with datasets (example 2 above), but, it is possible to use a combination of other rule keywords. Keep in mind the cost of additional keywords though e.g. in the second example rule above, negative performance impact can be expected due to pcrexform.

8.44.2.2. datarep

Data Reputation allows matching data against a reputation list.

Syntax:

datarep:<name>,<operator>,<value>, \
    [, load <file name>, type <string|md5|sha256|ipv4|ip>, memcap <size>, hashsize <size>];

Example rules could look like:

alert dns any any -> any any (dns.query; to_md5; datarep:dns_md5, >, 200, load dns_md5.rep, type md5, memcap 100mb, hashsize 2048; sid:1;)
alert dns any any -> any any (dns.query; to_sha256; datarep:dns_sha256, >, 200, load dns_sha256.rep, type sha256; sid:2;)
alert dns any any -> any any (dns.query; datarep:dns_string, >, 200, load dns_string.rep, type string; sid:3;)

In these examples the DNS query string is checked against three different reputation lists. A MD5 list, a SHA256 list, and a raw string (buffer) list. The rules will only match if the data is in the list and the reputation value is higher than 200.

8.44.3. Rule Reloads

Sets that are defined in the yaml, or sets that only use state or save, are considered dynamic sets. These are not reloaded during rule reloads.

Sets that are defined in rules using only load are considered static tests. These are not expected to change during runtime. During rule reloads these are reloaded from disk. This reload is effective when the complete rule reload process is complete.

8.44.4. Unix Socket

8.44.4.1. dataset-add

Unix Socket command to add data to a set. On success, the addition becomes active instantly.

Syntax:

dataset-add <set name> <set type> <data>
set name

Name of an already defined dataset

type

Data type: string, md5, sha256, ipv4, ip

data

Data to add in serialized form (base64 for string, hex notation for md5/sha256, string representation for ipv4/ip)

Example adding 'google.com' to set 'myset':

dataset-add myset string Z29vZ2xlLmNvbQ==

8.44.4.2. dataset-remove

Unix Socket command to remove data from a set. On success, the removal becomes active instantly.

Syntax:

dataset-remove <set name> <set type> <data>
set name

Name of an already defined dataset

type

Data type: string, md5, sha256, ipv4, ip

data

Data to remove in serialized form (base64 for string, hex notation for md5/sha256, string representation for ipv4/ip)

8.44.4.3. dataset-clear

Unix Socket command to remove all data from a set. On success, the removal becomes active instantly.

Syntax:

dataset-clear <set name> <set type>
set name

Name of an already defined dataset

type

Data type: string, md5, sha256, ipv4, ip

8.44.4.4. dataset-lookup

Unix Socket command to test if data is in a set.

Syntax:

dataset-lookup <set name> <set type> <data>
set name

Name of an already defined dataset

type

Data type: string, md5, sha256, ipv4, ip

data

Data to test in serialized form (base64 for string, hex notation for md5/sha256, string notation for ipv4/ip)

Example testing if 'google.com' is in the set 'myset':

dataset-lookup myset string Z29vZ2xlLmNvbQ==

8.44.4.5. dataset-dump

Unix socket command to trigger a dump of datasets to disk.

Syntax:

dataset-dump

8.44.5. File formats

Datasets use a simple CSV format where data is per line in the file.

8.44.5.1. data types

string

in the file as base64 encoded string

md5

in the file as hex encoded string

sha256

in the file as hex encoded string

ipv4

in the file as string

ip

in the file as string, it can be IPv6 or IPv4 address (standard notation or IPv4 in IPv6 one)

8.44.5.2. dataset

Datasets have a simple structure, where there is one piece of data per line in the file.

Syntax:

<data>

e.g. for ua-seen with type string:

TW96aWxsYS80LjAgKGNvbXBhdGlibGU7ICk=

which when piped to base64 -d reveals its value:

Mozilla/4.0 (compatible; )

8.44.5.3. datarep

The datarep format follows the dataset, expect that there are 1 more CSV field:

Syntax:

<data>,<value>

8.44.6. File Locations

Dataset filenames configured in the suricata.yaml can exist anywhere on your filesytem.

When a dataset filename is specified in rule, the following rules are applied:

  • For load, the filename is opened relative to the rule file containing the rule. Absolute filenames and parent directory traversals are allowed.

  • For save and state the filename is relative to $LOCALSTATEDIR/suricata/data. On many installs this will be /var/lib/suricata/data, but run suricata --build-info and check the value of --localstatedir to verify this location onn your installation.

    • Absolute filenames, or filenames containing parent directory traversal (..) are not allowed unless the configuration paramater datasets.allow-absolute-filenames is set to true.

8.44.7. Security

As datasets potentially allow a rule distributor write access to your system with save and state dataset rules, the locations allowed are strict by default, however there are two dataset options to tune the security of rules utilizing dataset filenames:

datasets:
  rules:
    # Set to true to allow absolute filenames and filenames that use
    # ".." components to reference parent directories in rules that specify
    # their filenames.
    allow-absolute-filenames: false

    # Allow datasets in rules write access for "save" and
    # "state". This is enabled by default, however write access is
    # limited to the data directory.
    allow-write: true

By setting datasets.rules.allow-write to false, all save and state rules will fail to load. This option is enabled by default to preserve compatiblity with previous 6.0 Suricata releases, however may change in a future major release.

Pre-Suricata 6.0.13 behavior can be restored by setting datasets.rules.allow-absolute-filenames to true, however allowing so will allow any rule to overwrite any file on your system that Suricata has write access to.