plyara

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Parse YARA rules into a dictionary representation.

Plyara is a script and library that lexes and parses a file consisting of one more YARA rules into a python dictionary representation. The goal of this tool is to make it easier to perform bulk operations or transformations of large sets of YARA rules, such as extracting indicators, updating attributes, and analyzing a corpus. Other applications include linters and dependency checkers.

Plyara leverages the Python module PLY for lexing YARA rules.

This is a community-maintained fork of the original plyara by 8u1a. The “plyara” trademark is used with permission.

Installation

Plyara requires Python 3.5+.

Install with pip:

pip install plyara

Usage

Use the plyara Python library in your own applications:

>>> import plyara
>>> parser = plyara.Plyara()
>>> mylist = parser.parse_string('rule MyRule { strings: $a="1" \n condition: false }')
>>>
>>> import pprint
>>> pprint.pprint(mylist)
[{'condition_terms': ['false'],
  'raw_condition': 'condition: false ',
  'raw_strings': 'strings: $a="1" \n ',
  'rule_name': 'MyRule',
  'start_line': 1,
  'stop_line': 2,
  'strings': [{'name': '$a', 'type': 'text', 'value': '1'}]}]
>>>

Or, use the included plyara script from the command line:

$ plyara -h
usage: plyara [-h] [--log] FILE

Parse YARA rules into a dictionary representation.

positional arguments:
  FILE        File containing YARA rules to parse.

optional arguments:
  -h, --help  show this help message and exit
  --log       Enable debug logging to the console.

The command-line tool will print valid JSON output when parsing rules:

$ cat example.yar
rule silent_banker : banker
{
    meta:
        description = "This is just an example"
        thread_level = 3
        in_the_wild = true
    strings:
        $a = {6A 40 68 00 30 00 00 6A 14 8D 91}
        $b = {8D 4D B0 2B C1 83 C0 27 99 6A 4E 59 F7 F9}
        $c = "UVODFRYSIHLNWPEJXQZAKCBGMT"
    condition:
        $a or $b or $c
}

$ plyara example.yar
[
    {
        "condition_terms": [
            "$a",
            "or",
            "$b",
            "or",
            "$c"
        ],
        "metadata": [
            {
                "description": "This is just an example"
            },
            {
                "thread_level": 3
            },
            {
                "in_the_wild": true
            }
        ],
        "raw_condition": "condition:\n        $a or $b or $c\n",
        "raw_meta": "meta:\n        description = \"This is just an example\"\n        thread_level = 3\n        in_the_wild = true\n    ",
        "raw_strings": "strings:\n        $a = {6A 40 68 00 30 00 00 6A 14 8D 91}\n        $b = {8D 4D B0 2B C1 83 C0 27 99 6A 4E 59 F7 F9}\n        $c = \"UVODFRYSIHLNWPEJXQZAKCBGMT\"\n    ",
        "rule_name": "silent_banker",
        "start_line": 1,
        "stop_line": 13,
        "strings": [
            {
                "name": "$a",
                "type": "byte",
                "value": "{6A 40 68 00 30 00 00 6A 14 8D 91}"
            },
            {
                "name": "$b",
                "type": "byte",
                "value": "{8D 4D B0 2B C1 83 C0 27 99 6A 4E 59 F7 F9}"
            },
            {
                "name": "$c",
                "type": "text",
                "value": "UVODFRYSIHLNWPEJXQZAKCBGMT"
            }
        ],
        "tags": [
            "banker"
        ]
    }
]

Migration

If you used an older version of plyara, and want to migrate to this version, there will be some changes required. Most importantly, the parser object instantiation has changed. It was:

# Old style - don't do this!
import plyara.interp as interp
rules_list = interp.parseString(open('myfile.yar').read())

But is now:

# New style - do this instead!
import plyara
parser = plyara.Plyara()
rules_list = parser.parse_string(open('myfile.yar').read())

The existing parsed keys have stayed the same, and new ones have been added.

When reusing a parser for multiple rules and/or files, be aware that imports are now shared across all rules - if one rule has an import, that import will be added to all rules in your parser object.

Contributing

  • If you find a bug, or would like to see a new feature, Pull Requests and Issues are always welcome.
  • By submitting changes, you agree to release those changes under the terms of the LICENSE.
  • Writing passing unit tests for your changes, while not required, is highly encouraged and appreciated.

Discussion

  • You may join our IRC channel on irc.freenode.net #plyara
  • Additionally, project developers can join our slack http://plyara.slack.com (If you need an invite, please ask in the IRC channel.)

Module Documentation

class plyara.Plyara(console_logging=False, store_raw_sections=True)

Bases: plyara.core.Parser

Define the lexer and the parser rules.

class plyara.core.Parser(console_logging=False, store_raw_sections=True)

Bases: object

Interpret the output of the parser and produce an alternative representation of YARA rules.

plyara utility functions.

This module contains various utility functions for working with plyara output.

plyara.utils.detect_dependencies(rule)

Take a parsed yararule and provide a list of external rule dependencies.

Args:
rule: Dict output from a parsed rule.
Returns:
list: External rule dependencies.
plyara.utils.detect_imports(rule)

Take a parsed yararule and provide a list of required imports based on condition.

Args:
rule: Dict output from a parsed rule.
Returns:
list: Imports that are required.
plyara.utils.generate_logic_hash(rule)

Calculate hash value of rule strings and condition.

Args:
rule: Dict output from a parsed rule.
Returns:
str: Hexdigest SHA1.
plyara.utils.is_valid_rule_name(entry)

Check to see if entry is a valid rule name.

Args:
entry: String containing rule name.
Returns:
bool
plyara.utils.is_valid_rule_tag(entry)

Check to see if entry is a valid rule tag.

Args:
entry: String containing tag.
Returns:
bool
plyara.utils.rebuild_yara_rule(rule)

Take a parsed yararule and rebuild it into a usable one.

Args:
rule: Dict output from a parsed rule.
Returns:
str: Formatted text string of YARA rule.

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