Sigma Importer

Sigma Importer (a.k.a. sigmai) is a project designed to do the opposite of Sigma. The objective of sigmai is to convert specific data sources into the Sigma generic and open signature format.

Installation

If you have Go installed, you can get the newest version of sigmai through:

go get github.com/0xThiebaut/sigmai

Alternatively, you can download the release binaries which are updated less frequently.

Usage

For the generic usage's help section, sigmai is equipped with the --help flag (shorthand -h).

sigmai --help

Usage of ./sigmai:
      --directory-path string       Directory: Path to save rules
  -h, --help                        Display this help section
  -i, --interval string             Continuous importing interval
      --json                        Output JSON instead of pretty print
      --level-set string            Set level on all rules [low, medium, high, critical]
      --misp-buffer int             MISP: Size of the event buffer (default 500)
      --misp-events ints            MISP: Only events with matching IDs
      --misp-ids-exclude            MISP: Only IDS-disabled attributes
      --misp-ids-ignore             MISP: All attributes regardless of their IDS flag
      --misp-insecure               MISP: Allow insecure connections when using SSL
      --misp-key string             MISP: User API key
      --misp-keywords stringArray   MISP: All events containing any of the keywords
      --misp-levels stringArray     MISP: Only events with matching threat levels [1-4]
      --misp-period strings         MISP: Only events within time-frame (4d, 3w, ...)
      --misp-published              MISP: Only published events
      --misp-published-exclude      MISP: Only unpublished events
      --misp-tags stringArray       MISP: Only events with matching tags
      --misp-url string             MISP: Instance API base URL
      --misp-warning-include        MISP: Include attributes listed on warning-list
      --misp-workers int            MISP: Number of concurrent workers (default 20)
  -q, --quiet                       Only output error information
  -s, --source string               Source backend [misp]
      --status-set string           Set status on all rules [experimental, testing, stable]
      --tags-add stringArray        Add tags on all rules
      --tags-clear                  Clear tags from all rules
      --tags-rm stringArray         Remove tags from all rules
      --tags-set stringArray        Set tags on all rules
  -t, --target string               Target backend [stdout, directory] (default "stdout")
  -v, --verbose                     Show debug information

Sources

A source is the origin from which data will be fetched in order to generate Sigma rules. Currently, MISP is the only implemented source.

A source can be defined through the --source flag (shorthand -s). Currently, the only acceptable value for this flag is misp.

MISP

Importing events from MISP can be done by specifying misp as source. When using MISP, The following flags are required:

Flag	Description
--misp-url	The URL at which the MISP instance API can be queried (i.e. https://localhost).
--misp-key	A User API key authorized to query the MISP instance.

Use Cases

A sample sigmai command would be as follows:

sigmai -t stdout -s misp --misp-url https://localhost --misp-key CAFEBABE== --misp-levels 1,2

The above command sends the Sigma rules to the stdout target (-t; more on that later). The Sigma rules are to be generated from the misp source (-s). In MISP, we'll solely generate Sigma rules for event's with a level (--misp-levels) of high (1) or medium (2). For the eligible events, only attributes flagged for IDS (decent enough for detection) will be used. Furthermore, any attribute on a warning list (a.k.a. subject to false positives) won't be included.

As an example, this is how a generated multi-document Sigma rule would look like if imported from MISP:

action: global
title: 'OSINT: Emissary Panda – A potential new malicious tool'
id: 5b0562d3-8460-4482-93c4-05a3ac12042b
status: experimental
description: See MISP event 60870
author: dcso.de
level: medium
tags:
- APT
- tlp:white
- iep:traffic-light-protocol="WHITE"
- DCSO:tie="ALL"
- DCSO:sharing="PUBLIC"
- osint:source-type="blog-post"
---
logsource:
  product: windows
detection:
  condition:
  - event60870
  - all of event60870attr2049468mapping*
  - event60870object33488
  - event60870object33489
  - event60870object33490 and all of event60870object33490attr2049523mapping*
  - event60870object33491 and all of event60870object33491attr2049526mapping*
  event60870:
    DestinationIp:
    - 159.65.80.157
    - 103.59.144.183
  event60870attr2049468mappingFilename:
  - Image|endswith: '%APPDATA%\systemconfig\sys.bin.url'
  - ParentImage|endswith: '%APPDATA%\systemconfig\sys.bin.url'
  - CommandLine|contains: '%APPDATA%\systemconfig\sys.bin.url'
  - ParentCommandLine|contains: '%APPDATA%\systemconfig\sys.bin.url'
  - ProcessName: '%APPDATA%\systemconfig\sys.bin.url'
  - ParentProcessName: '%APPDATA%\systemconfig\sys.bin.url'
  event60870object33488:
    Hashes|contains:
    - c69d60b82252b6e7eaaeb710d5e1ebe5
    - 4c0211c91b4b9f99e52f4d385e6e3960b321a3b0
    - 4d65d371a789aabe1beadcc10b38da1f998cd3ec87d4cc1cfbf0af014b783822
    - 768:NHO6X9W62QIPe1HhDIRmnTEDtcvyvfSl0zeM:NHOymWBDLYg0zB
  event60870object33489:
    Hashes|contains: 93b972951685b4ae284583dbc3959725
  event60870object33490:
    Hashes|contains: 2b2bb4c132d808572f180fe4db3a0a3143a37fdece667f8e78778ee1e9717606
  event60870object33490attr2049523mappingFilename:
  - Image|endswith: sys.bin.url
  - ParentImage|endswith: sys.bin.url
  - CommandLine|contains: sys.bin.url
  - ParentCommandLine|contains: sys.bin.url
  - ProcessName: sys.bin.url
  - ParentProcessName: sys.bin.url
  event60870object33491:
    Hashes|contains: 3e718f39dfb2f6b8fba366fefa8b7c127db1e6795f3caad2d4a9f3753eea0adc
  event60870object33491attr2049526mappingFilename:
  - Image|endswith: sys.bin.url
  - ParentImage|endswith: sys.bin.url
  - CommandLine|contains: sys.bin.url
  - ParentCommandLine|contains: sys.bin.url
  - ProcessName: sys.bin.url
  - ParentProcessName: sys.bin.url
---
// Many more log-sources (firewall, proxy, webserver, ...) are trimmed for readability...

Specific Events

Alternatively, you might wish to import a specific set of events. To do so, you might use the --misp-events flag as follows:

sigmai -t stdout -s misp --misp-url https://localhost --misp-key CAFEBABE== --misp-events 123,456,789

The above command will import the events with IDs 123, 456 and 789.

Searching Events

You can also import events whose description contains one of the specified case-sensitive sub-string. To do so, you would need to use the --misp-keywords flag as follows:

sigmai -t stdout -s misp --misp-url https://localhost --misp-key CAFEBABE== --misp-keywords emotet,zloader

The above command will import all events whose description contains either the emotet or zloader substring.

Targets

A target is a way to select where to send the generated Sigma rules.

Defining the target can be done using the --target flag (shorthand -t). Currently, both stdout and directory are implemented.

Stdout

This target outputs the generated Sigma rules to the standard output. It can be selected by using stdout as the --target flag's value.

Do note that all other logging is send to the standard error, which enables you to split logging and generated Sigma rules.

Directory

This target output's the generated Sigma rules into a directory, which defaults to the current one. It can be selected by using directory as the --target flag's value.

Additionally, one may change the path using the --directory-path flag.

Modifiers

The sigmai tool comes with some additional modifiers to ensure the generated rules meet your existing standard.

Tags

More specifically, one can modify the imported rule's tags by using the beneath flags.

Flag	Description
--tags-add	A flag with a comma-separated list of tags to be added to the current ones.
--tags-rm	A flag with a comma-separated list of tags to be removed if present in the current ones.
--tags-set	A flag with a comma-separated list of tags to overwrite the current ones.
--tags-clear	A flag clearing all tags, resulting in tag-less rules.

Level

You can also override the rules by defining a common level using the --level-set flag.

Status

As for levels, sigmai enables you to override the status of all rules by using the --status-set flag.

Continuous Importing

It is possible to run sigmai continuously a bit like a cron job would. The --interval flag (shorthand -i) defines an interval at which an import should be done.

This flag can be combined with source's period-filters such as MISP's --misp-period flag. As an example, the beneath command will import the last 15 minutes of MISP events as Sigma rules every 10 minutes.

sigmai -t directory --directory-path ~/rules -i 10m -s misp --misp-url https://localhost --misp-key CAFEBABE== --misp-period 15m

Tips & Tricks

Filter Your Queries

The sigmai-generated queries will hopefully cover more cases (log-sources, platforms, ...) than you actually need. Did you know that when compiling the Sigma rules with sigmac, you can filter rules to match your use-cases through the --filter flag (shorthand -f)?

Acknowledgements

Development of this project has been supported by NVISO Labs. Interested in this project? You might fit with us!

Many thanks to Florian Roth for his valuable feedback and without whom we wouldn't have Sigma in the first place.

License

© Maxime Thiebaut, 2020 — Licensed under the EUPL.