Windows.Detection.Yara.NTFS

This artifact searches the MFT, returns a list of target files then runs Yara over the target list.

There are 3 kinds of Yara rules that can be deployed:

1. Url link to a yara rule.
2. Shorthand yara in the format wide nocase ascii:string1,string2,string3.
3. or a Standard Yara rule attached as a parameter.

Only one method of Yara will be applied and search order is as above.

The artifact leverages Windows.NTFS.MFT so similar regex filters can be applied including Path, Size and date. The artifact also has an option to search across all attached drives and upload any files with Yara hits.

Some examples of path regex may include:

• Extension at a path: C:\\Windows\\System32\\.+\.dll$
• More wildcards: Windows\\.+\\.+\.dll$
• Specific file: Windows\\System32\\kernel32\.dll$
• Multiple extentions: \.(php|aspx|resx|asmx)$

Note: no drive and forward slashes - these expressions are for paths relative to the root of the filesystem. If upload is selected NumberOfHits is redundant and not advised as hits are grouped by path to ensure files only downloaded once.

name: Windows.Detection.Yara.NTFS
author: Matt Green - @mgreen27
description: |
  This artifact searches the MFT, returns a list of target files then runs Yara
  over the target list.

  There are 3 kinds of Yara rules that can be deployed:

  1. Url link to a yara rule.
  2. Shorthand yara in the format `wide nocase ascii:string1,string2,string3`.
  3. or a Standard Yara rule attached as a parameter.

  Only one method of Yara will be applied and search order is as above.

  The artifact leverages Windows.NTFS.MFT so similar regex filters can be applied
  including Path, Size and date. The artifact also has an option to search across
  all attached drives and upload any files with Yara hits.

  Some examples of path regex may include:

  * Extension at a path: `C:\\Windows\\System32\\.+\.dll$`
  * More wildcards: `Windows\\.+\\.+\.dll$`
  * Specific file: `Windows\\System32\\kernel32\.dll$`
  * Multiple extentions: `\.(php|aspx|resx|asmx)$`

  Note: no drive and forward slashes - these expressions are for paths
  relative to the root of the filesystem.
  If upload is selected NumberOfHits is redundant and not advised as hits are
  grouped by path to ensure files only downloaded once.

type: CLIENT
parameters:
  - name: FileNameRegex
    description: Only file names that match this regular expression will be scanned.
    default: ^kernel32\.dll$
  - name: PathRegex
    description: Only paths that match this regular expression will be scanned.
    default: C:\\Windows\\System32\\
  - name: DriveLetter
    description: "Target drive. Default is a C:"
    default: "C:"
  - name: SizeMax
    type: int
  - name: SizeMin
    type: int
  - name: AllDrives
    type: bool
  - name: UploadHits
    type: bool
  - name: EarliestSILastChanged
    type: timestamp
  - name: LatestSILastChanged
    type: timestamp
  - name: EarliestFNCreation
    type: timestamp
  - name: LatestFNCreation
    type: timestamp
  - name: YaraUrl
    description: If configured will attempt to download Yara rules form Url
    default:
    type: upload
  - name: YaraRule
    type: yara
    description: Final Yara option and the default if no other options provided.
    default: |
        rule IsPE:TestRule {
           meta:
              author = "the internet"
              date = "2021-03-04"
              description = "A simple PE rule to test yara features"
          condition:
             uint16(0) == 0x5A4D and
             uint32(uint32(0x3C)) == 0x00004550
        }
  - name: NumberOfHits
    description: THis artifact will stop by default at one hit. This setting allows additional hits
    default: 1
    type: int64
  - name: ContextBytes
    description: Include this amount of bytes around hit as context.
    default: 0
    type: int


sources:
  - precondition:
      SELECT OS From info() where OS = 'windows'

    query: |
      -- check which Yara to use
      LET yara_rules = YaraUrl || YaraRule

      -- first find all matching files mft
      LET files = SELECT
            OSPath, IsDir
        FROM Artifact.Windows.NTFS.MFT(
            MFTDrive=DriveLetter, AllDrives=AllDrives,
            FileRegex=FileNameRegex,PathRegex=PathRegex,
            SizeMax=SizeMax, SizeMin=SizeMin)
        WHERE NOT IsDir
            AND NOT OSPath =~ '''\\\\.\\.:\\<Err>\\'''
            AND if(condition=EarliestSILastChanged,
                then= LastRecordChange0x10 > EarliestSILastChanged,
                else= True)
            AND if(condition=LatestSILastChanged,
                then= LastRecordChange0x10 < LatestSILastChanged,
                else= True)
            AND if(condition=EarliestFNCreated,
                then= Created0x30 > EarliestFNCreation,
                else= True)
            AND if(condition=LatestFNCreated,
                then= Created0x30 < LatestFNCreation,
                else= True)

      -- scan files and only report a single hit.
      LET hits = SELECT * FROM foreach(row=files,
            query={
                SELECT
                    FileName, OSPath,
                    File.Size AS Size,
                    File.ModTime AS ModTime,
                    Rule, Tags, Meta,
                    String.Name as YaraString,
                    String.Offset as HitOffset,
                    if(condition=String.Data,
                       then=upload(
                            accessor='scope',
                            file='String.Data',
                            name=format(format="%v-%v-%v",
                            args=[
                                OSPath,
                                if(condition= String.Offset - ContextBytes < 0,
                                    then= 0,
                                    else= String.Offset - ContextBytes),
                                if(condition= String.Offset + ContextBytes > File.Size,
                                    then= File.Size,
                                    else= String.Offset + ContextBytes) ]
                            ))) as HitContext
                FROM yara(rules=yara_rules,
                   files=OSPath, context=ContextBytes, number=NumberOfHits)
            })

      -- upload files that have hit
      LET upload_hits=SELECT *,
            upload(file=OSPath) AS Upload
        FROM hits
        GROUP BY OSPath

      -- return rows
      SELECT * FROM if(condition=UploadHits,
        then={ SELECT * FROM upload_hits},
        else={ SELECT * FROM hits})

column_types:
  - name: HitContext
    type: preview_upload