yara-scanner 1.0.16

A Python wrapper library for libyara and a local server for fully utilizing the CPUs of the system to scan with yara.

Yara Scanner

A wrapper around the yara-python project the provides the following capabilities.

• Change tracking of yara files, directories of yara files, or git repositories of yara files.
• File and data scanning with the ability to filter based on meta data matching.
• Distributed scanning processes that maximize the use of multi-core systems.
• Command line interface.

Python Examples

Loading a single yara file and then scanning data.

from pprint import pprint
from yara_scanner import YaraScanner

scanner = YaraScanner()
# tells the scanner to start tracking this yara file
scanner.track_yara_file('my_rules.yar')
scanner.load_rules()
if scanner.scan('/path/to/scan_target.txt'):
   pprint(scanner.scan_results)
   
# this returns True if any tracked yara files have changed
if scanner.check_rules():
   scanner.load_rules()

Installation Instructions

pip install yara-scanner

Command Line Instructions

usage: scan [-h] [-r] [--from-stdin] [--debug] [-j] [-t] [-y YARA_RULES]
            [-Y YARA_DIRS] [-G YARA_REPOS] [-c] [-b BLACKLISTED_RULES]
            [-B BLACKLISTED_RULES_PATH] [-d SIGNATURE_DIR]
            [PATHS [PATHS ...]]

Scan the given file with yara using all available rulesets.

positional arguments:
  PATHS                 One or more files or directories to scan with yara.

optional arguments:
  -h, --help            show this help message and exit
  -r, --recursive       Recursively scan directories.
  --from-stdin          Read the list of files to scan from stdin.
  --debug               Log debug level messages.
  -j, --dump-json       Dump JSON details of matches. Otherwise just list the
                        rules that hit.
  -t, --test            Test each yara file separately against different types
                        of buffers for performance issues.
  -y YARA_RULES, --yara-rules YARA_RULES
                        One yara rule to load. You can specify more than one
                        of these.
  -Y YARA_DIRS, --yara-dirs YARA_DIRS
                        One directory containing yara rules to load. You can
                        specify more than one of these.
  -G YARA_REPOS, --yara-repos YARA_REPOS
                        One directory that is a git repository that contains
                        yara rules to load. You can specify more than one of
                        these.
  -c, --compile-only    Compile the rules and exit.
  -b BLACKLISTED_RULES, --blacklist BLACKLISTED_RULES
                        A rule to blacklist (remove from the results.) You can
                        specify more than one of these options.
  -B BLACKLISTED_RULES_PATH, --blacklist-path BLACKLISTED_RULES_PATH
                        Path to a file that contains a list of rules to
                        blacklist, one per line.

Command Line Examples

• scan a single file

  scan ms0day.ppsx
  

• scan a single file and generate JSON output

  scan -j ms0day.ppsx
  scan -j ms0day.ppsx | json_pp
  

• scan multiple files

  scan file1 file2 file3
  

• scan all files in a directory and all sub-directories

  scan -r dir
  

• scan a list of files passed in on standard input

  find dridex -type f | scan --from-stdin
  

• scan a single file with a single yara rule

  scan -y myrule.yar target_file
  

• scan a single file with all rules in a given directory

  scan -Y my_rule_dir target_file
  

• check the syntax of all the rules in a given directory

  scan -c -Y my_rule_dir
  

Blacklisting

The scan tool also supports "blacklisting" rules. These are specified by using the -b and -B command line options. These allow you to exclude certain rules from the search results rather than making changes to the rules themselves. We use this technique to allow us to use the open source yara repository as-is, rather than trying to maintain a modified branch.

Rule Output Selection

You can specify when a rule should (or should not) be displayed. This allows you to prevent some rules from matching against certain kinds of files, or for a rule to be matched against only one specific file.

The rules are specified as metadata name and value pairs. (example rule syntax)

rule html_rule: odd html
{
meta:
   mime_type = "text/html"
strings:
   ...
condition:
   ...
}

Metadata Names and Descriptions

file_ext   | Matches everything past the first period in the file name.
file_name  | Matches the full name of the file (not including the path.)
full_path  | Matches against the full path of the file, if one was specified.
mime_type  | Matches against the output of file -b --mime-type.

The value of the metadata variable is the string to match. By default the library matches as is, but special modifiers can be used to perform sub string matching and regular expressions. ** Special modifiers are added to the beginning of the value (or list of values) and apply to all values in the string. **

Matching Modifiers

!     | negation    | Negates the match. This can be placed before other modifiers.
sub:  | sub-search  | Match if this string appears anywhere.
re:   | regex       | Match if the regular expression is satisfied.

Values can be a comma separated list of values, regardless of the modifiers. Therefor, commas cannot be used in the patterns.

Rule Selection Examples

Only match files the end with the .exe extension.

file_ext = "exe"

Only match files that end with .exe, .dll or .ocx extension.

file_ext = "exe, dll, ocx"

Only match files that do not end with .exe, .dll or .ocx extension.

file_ext = "!exe, dll, ocx"

Only matches files that do not end with .bmp.

file_ext = "!bmp"

Only match files identified as PDF despite the file name.

mime_type = "application/pdf"

Only match files not identified as images.

mime_type = "!sub:image/"

Only match files that look like an invoice phish.

file_name = "re:invoice[0-9]+\\.doc$"

Only match files in a subdirectory called /ole.

full_path = "sub:/ole/"