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PyCIRCLean/bin/filecheck.py

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
import os
import mimetypes
import shlex
import subprocess
import zipfile
import argparse
import oletools.oleid
import olefile
import officedissector
import warnings
import exifread
from PIL import Image
# from PIL import PngImagePlugin
from pdfid import PDFiD, cPDFiD
from kittengroomer import FileBase, KittenGroomerBase, GroomerLogger
SEVENZ_PATH = '/usr/bin/7z'
class Config:
"""Configuration information for Filecheck."""
# Application subtypes (mimetype: 'application/<subtype>')
mimes_ooxml = ['vnd.openxmlformats-officedocument.']
mimes_office = ['msword', 'vnd.ms-']
mimes_libreoffice = ['vnd.oasis.opendocument']
mimes_rtf = ['rtf', 'richtext']
mimes_pdf = ['pdf', 'postscript']
mimes_xml = ['xml']
mimes_ms = ['dosexec']
mimes_compressed = ['zip', 'rar', 'bzip2', 'lzip', 'lzma', 'lzop',
'xz', 'compress', 'gzip', 'tar']
mimes_data = ['octet-stream']
# Image subtypes
mimes_exif = ['image/jpeg', 'image/tiff']
mimes_png = ['image/png']
# Mimetypes with metadata
mimes_metadata = ['image/jpeg', 'image/tiff', 'image/png']
# Commonly used malicious extensions
# Sources: http://www.howtogeek.com/137270/50-file-extensions-that-are-potentially-dangerous-on-windows/
# https://github.com/wiregit/wirecode/blob/master/components/core-settings/src/main/java/org/limewire/core/settings/FilterSettings.java
malicious_exts = (
# Applications
".exe", ".pif", ".application", ".gadget", ".msi", ".msp", ".com", ".scr",
".hta", ".cpl", ".msc", ".jar",
# Scripts
".bat", ".cmd", ".vb", ".vbs", ".vbe", ".js", ".jse", ".ws", ".wsf",
".wsc", ".wsh", ".ps1", ".ps1xml", ".ps2", ".ps2xml", ".psc1", ".psc2",
".msh", ".msh1", ".msh2", ".mshxml", ".msh1xml", ".msh2xml",
# Shortcuts
".scf", ".lnk", ".inf",
# Other
".reg", ".dll",
# Office macro (OOXML with macro enabled)
".docm", ".dotm", ".xlsm", ".xltm", ".xlam", ".pptm", ".potm", ".ppam",
".ppsm", ".sldm",
# banned from wirecode
".asf", ".asx", ".au", ".htm", ".html", ".mht", ".vbs",
".wax", ".wm", ".wma", ".wmd", ".wmv", ".wmx", ".wmz", ".wvx",
)
# Aliases
aliases = {
# Win executables
'application/x-msdos-program': 'application/x-dosexec',
'application/x-dosexec': 'application/x-msdos-program',
# Other apps with confusing mimetypes
'application/rtf': 'text/rtf',
}
# Sometimes, mimetypes.guess_type gives unexpected results, such as for .tar.gz files:
# In [12]: mimetypes.guess_type('toot.tar.gz', strict=False)
# Out[12]: ('application/x-tar', 'gzip')
# It works as expected if you do mimetypes.guess_type('application/gzip', strict=False)
override_ext = {'.gz': 'application/gzip'}
class File(FileBase):
def __init__(self, src_path, dst_path, logger):
super(File, self).__init__(src_path, dst_path)
self.is_recursive = False
self.logger = logger
subtypes_apps = [
(Config.mimes_office, self._winoffice),
(Config.mimes_ooxml, self._ooxml),
(Config.mimes_rtf, self.text),
(Config.mimes_libreoffice, self._libreoffice),
(Config.mimes_pdf, self._pdf),
(Config.mimes_xml, self.text),
(Config.mimes_ms, self._executables),
(Config.mimes_compressed, self._archive),
(Config.mimes_data, self._binary_app),
]
self.app_subtype_methods = self._make_method_dict(subtypes_apps)
types_metadata = [
(Config.mimes_exif, self._metadata_exif),
(Config.mimes_png, self._metadata_png),
]
self.metadata_mimetype_methods = self._make_method_dict(types_metadata)
self.mime_processing_options = {
'text': self.text,
'audio': self.audio,
'image': self.image,
'video': self.video,
'application': self.application,
'example': self.example,
'message': self.message,
'model': self.model,
'multipart': self.multipart,
'inode': self.inode,
}
def _check_dangerous(self):
if not self.has_mimetype:
self.make_dangerous('no mimetype')
if not self.has_extension:
self.make_dangerous('no extension')
if self.extension in Config.malicious_exts:
self.make_dangerous('malicious_extension')
def _check_extension(self):
"""
Guess the file's mimetype based on its extension.
If the file's mimetype (as determined by libmagic) is contained in
the `mimetype` module's list of valid mimetypes and the expected
mimetype based on its extension differs from the mimetype determined
by libmagic, then mark the file as dangerous.
"""
if self.extension in Config.override_ext:
expected_mimetype = Config.override_ext[self.extension]
else:
expected_mimetype, encoding = mimetypes.guess_type(self.src_path,
strict=False)
if expected_mimetype in Config.aliases:
expected_mimetype = Config.aliases[expected_mimetype]
is_known_extension = self.extension in mimetypes.types_map.keys()
if is_known_extension and expected_mimetype != self.mimetype:
# LOG: improve this string
self.make_dangerous('expected_mimetype')
def _check_mimetype(self):
"""
Compare mimetype (as determined by libmagic) to extension.
Determine whether the extension that are normally associated with
the mimetype include the file's actual extension.
"""
if self.mimetype in Config.aliases:
mimetype = Config.aliases[self.mimetype]
else:
mimetype = self.mimetype
expected_extensions = mimetypes.guess_all_extensions(mimetype,
strict=False)
if expected_extensions:
if self.has_extension and self.extension not in expected_extensions:
# LOG: improve this string
self.make_dangerous('expected extensions')
def _check_filename(self):
if self.filename[0] is '.':
# TODO: handle dotfiles?
pass
right_to_left_override = u"\u202E"
if right_to_left_override in self.filename:
self.make_dangerous('Filename contains dangerous character')
self.dst_path = self.dst_path.replace(right_to_left_override, '')
# TODO: change self.filename and'filename' property?
def check(self):
self._check_dangerous()
self._check_filename()
if self.has_extension:
self._check_extension()
if self.has_mimetype:
self._check_mimetype()
if not self.is_dangerous:
self.mime_processing_options.get(self.main_type, self.unknown)()
def write_log(self):
props = self.get_all_props()
self.logger.add_file(props)
# ##### Helper functions #####
def _make_method_dict(self, list_of_tuples):
"""Returns a dictionary with mimetype: method pairs."""
dict_to_return = {}
for list_of_subtypes, method in list_of_tuples:
for subtype in list_of_subtypes:
dict_to_return[subtype] = method
return dict_to_return
@property
def has_metadata(self):
"""True if filetype typically contains metadata, else False."""
if self.mimetype in Config.mimes_metadata:
return True
return False
def make_tempdir(self):
"""Make a temporary directory at self.tempdir_path."""
self.tempdir_path = self.dst_path + '_temp'
if not os.path.exists(self.tempdir_path):
os.makedirs(self.tempdir_path)
return self.tempdir_path
#######################
# ##### Discarded mimetypes, reason in the docstring ######
def inode(self):
"""Empty file or symlink."""
if self.is_symlink:
symlink_path = self.get_property('symlink')
self.add_file_string('Symlink to {}'.format(symlink_path))
else:
self.add_file_string('Inode file')
self.should_copy = False
def unknown(self):
"""Main type should never be unknown."""
self.add_file_string('Unknown file')
self.should_copy = False
def example(self):
"""Used in examples, should never be returned by libmagic."""
self.add_file_string('Example file')
self.should_copy = False
def multipart(self):
"""Used in web apps, should never be returned by libmagic"""
self.add_file_string('Multipart file')
self.should_copy = False
# ##### Treated as malicious, no reason to have it on a USB key ######
def message(self):
"""Process a message file."""
self.add_file_string('Message file')
self.make_dangerous('Message file')
def model(self):
"""Process a model file."""
self.add_file_string('Model file')
self.make_dangerous('Model file')
# ##### Files that will be converted ######
def text(self):
"""Process an rtf, ooxml, or plaintext file."""
for mt in Config.mimes_rtf:
if mt in self.sub_type:
self.add_file_string('Rich Text file')
# TODO: need a way to convert it to plain text
self.force_ext('.txt')
return
for mt in Config.mimes_ooxml:
if mt in self.sub_type:
self.add_file_string('OOXML File')
self._ooxml()
return
self.add_file_string('Text file')
self.force_ext('.txt')
def application(self):
"""Process an application specific file according to its subtype."""
for subtype, method in self.app_subtype_methods.items():
if subtype in self.sub_type:
# TODO: should we change the logic so we don't iterate through all of the subtype methods?
# TODO: should these methods return a value?
method()
self.add_file_string('Application file')
return
self.add_file_string('Unknown Application file')
self._unknown_app()
def _executables(self):
"""Process an executable file."""
# LOG: change the processing_type property to some other name or include in file_string
self.set_property('processing_type', 'executable')
self.make_dangerous('executable')
def _winoffice(self):
"""Process a winoffice file using olefile/oletools."""
# LOG: processing_type property
self.set_property('processing_type', 'WinOffice')
oid = oletools.oleid.OleID(self.src_path) # First assume a valid file
if not olefile.isOleFile(self.src_path):
# Manual processing, may already count as suspicious
try:
ole = olefile.OleFileIO(self.src_path, raise_defects=olefile.DEFECT_INCORRECT)
except:
self.make_dangerous('not parsable')
if ole.parsing_issues:
self.make_dangerous('parsing issues')
else:
if ole.exists('macros/vba') or ole.exists('Macros') \
or ole.exists('_VBA_PROJECT_CUR') or ole.exists('VBA'):
self.make_dangerous('macro')
else:
indicators = oid.check()
# Encrypted can be set by multiple checks on the script
if oid.encrypted.value:
self.make_dangerous('encrypted')
if oid.macros.value or oid.ole.exists('macros/vba') or oid.ole.exists('Macros') \
or oid.ole.exists('_VBA_PROJECT_CUR') or oid.ole.exists('VBA'):
self.make_dangerous('macro')
for i in indicators:
if i.id == 'ObjectPool' and i.value:
# TODO: Is it suspicious?
# LOG: user defined property
self.set_property('objpool', True)
elif i.id == 'flash' and i.value:
self.make_dangerous('flash')
def _ooxml(self):
"""Process an ooxml file."""
# LOG: processing_type property
self.set_property('processing_type', 'ooxml')
try:
doc = officedissector.doc.Document(self.src_path)
except Exception:
self.make_dangerous('invalid ooxml file')
return
# There are probably other potentially malicious features:
# fonts, custom props, custom XML
if doc.is_macro_enabled or len(doc.features.macros) > 0:
self.make_dangerous('macro')
if len(doc.features.embedded_controls) > 0:
self.make_dangerous('activex')
if len(doc.features.embedded_objects) > 0:
# Exploited by CVE-2014-4114 (OLE)
self.make_dangerous('embedded obj')
if len(doc.features.embedded_packages) > 0:
self.make_dangerous('embedded pack')
def _libreoffice(self):
"""Process a libreoffice file."""
self.set_property('processing_type', 'libreoffice')
# As long as there is no way to do a sanity check on the files => dangerous
try:
lodoc = zipfile.ZipFile(self.src_path, 'r')
except:
# TODO: are there specific exceptions we should catch here? Or is anything ok
self.make_dangerous('invalid libreoffice file')
for f in lodoc.infolist():
fname = f.filename.lower()
if fname.startswith('script') or fname.startswith('basic') or \
fname.startswith('object') or fname.endswith('.bin'):
self.make_dangerous('macro')
def _pdf(self):
"""Process a PDF file."""
# LOG: processing_type property
self.set_property('processing_type', 'pdf')
xmlDoc = PDFiD(self.src_path)
oPDFiD = cPDFiD(xmlDoc, True)
# TODO: are there other characteristics which should be dangerous?
if oPDFiD.encrypt.count > 0:
self.make_dangerous('encrypted pdf')
if oPDFiD.js.count > 0 or oPDFiD.javascript.count > 0:
self.make_dangerous('pdf with javascript')
if oPDFiD.aa.count > 0 or oPDFiD.openaction.count > 0:
self.make_dangerous('openaction')
if oPDFiD.richmedia.count > 0:
self.make_dangerous('flash')
if oPDFiD.launch.count > 0:
self.make_dangerous('launch')
def _archive(self):
"""
Process an archive using 7zip.
The archive is extracted to a temporary directory and self.process_dir
is called on that directory. The recursive archive depth is increased
to protect against archive bombs.
"""
# LOG: change this to something archive specific
self.set_property('processing_type', 'archive')
self.should_copy = False
self.is_recursive = True
def _unknown_app(self):
"""Process an unknown file."""
self.make_unknown()
def _binary_app(self):
"""Process an unknown binary file."""
self.make_binary()
#######################
# Metadata extractors
def _metadata_exif(self, metadata_file_path):
"""Read exif metadata from a jpg or tiff file using exifread."""
# TODO: this method is kind of long, can we shorten it somehow?
img = open(self.src_path, 'rb')
tags = None
try:
tags = exifread.process_file(img, debug=True)
except Exception as e:
self.add_error(e, "Error while trying to grab full metadata for file {}; retrying for partial data.".format(self.src_path))
if tags is None:
try:
tags = exifread.process_file(img, debug=True)
except Exception as e:
self.add_error(e, "Failed to get any metadata for file {}.".format(self.src_path))
img.close()
return False
for tag in sorted(tags.keys()):
# These tags are long and obnoxious/binary so we don't add them
if tag not in ('JPEGThumbnail', 'TIFFThumbnail'):
tag_string = str(tags[tag])
# Exifreader truncates data.
if len(tag_string) > 25 and tag_string.endswith(", ... ]"):
tag_value = tags[tag].values
tag_string = str(tag_value)
with open(metadata_file_path, 'w+') as metadata_file:
metadata_file.write("Key: {}\tValue: {}\n".format(tag, tag_string))
# LOG: how do we want to log metadata?
self.set_property('metadata', 'exif')
img.close()
return True
def _metadata_png(self, metadata_file_path):
"""Extract metadata from a png file using PIL/Pillow."""
warnings.simplefilter('error', Image.DecompressionBombWarning)
try:
img = Image.open(self.src_path)
for tag in sorted(img.info.keys()):
# These are long and obnoxious/binary
if tag not in ('icc_profile'):
with open(metadata_file_path, 'w+') as metadata_file:
metadata_file.write("Key: {}\tValue: {}\n".format(tag, img.info[tag]))
# LOG: handle metadata
self.set_property('metadata', 'png')
img.close()
except Exception as e: # Catch decompression bombs
# TODO: only catch DecompressionBombWarnings here?
self.add_error(e, "Caught exception processing metadata for {}".format(self.src_path))
self.make_dangerous('exception processing metadata')
return False
def extract_metadata(self):
"""Create metadata file and call correct metadata extraction method."""
metadata_file_path = self.create_metadata_file(".metadata.txt")
mt = self.mimetype
metadata_processing_method = self.metadata_mimetype_methods.get(mt)
if metadata_processing_method:
# TODO: should we return metadata and write it here instead of in processing method?
metadata_processing_method(metadata_file_path)
#######################
# ##### Media - audio and video aren't converted ######
def audio(self):
"""Process an audio file."""
self.log_string += 'Audio file'
self._media_processing()
def video(self):
"""Process a video."""
self.log_string += 'Video file'
self._media_processing()
def _media_processing(self):
"""Generic way to process all media files."""
self.set_property('processing_type', 'media')
def image(self):
"""
Process an image.
Extracts metadata to dest key using self.extract_metada() if metadata
is present. Creates a temporary directory on dest key, opens the image
using PIL.Image, saves it to the temporary directory, and copies it to
the destination.
"""
# TODO: make sure this method works for png, gif, tiff
if self.has_metadata:
self.extract_metadata()
tempdir_path = self.make_tempdir()
tempfile_path = os.path.join(tempdir_path, self.filename)
warnings.simplefilter('error', Image.DecompressionBombWarning)
try: # Do image conversions
img_in = Image.open(self.src_path)
img_out = Image.frombytes(img_in.mode, img_in.size, img_in.tobytes())
img_out.save(tempfile_path)
self.src_path = tempfile_path
except Exception as e: # Catch decompression bombs
# TODO: change this from all Exceptions to specific DecompressionBombWarning
self.add_error(e, "Caught exception (possible decompression bomb?) while translating file {}.".format(self.src_path))
self.make_dangerous()
self.add_file_string('Image file')
self.set_property('processing_type', 'image')
class KittenGroomerFileCheck(KittenGroomerBase):
def __init__(self, root_src, root_dst, max_recursive_depth=2, debug=False):
super(KittenGroomerFileCheck, self).__init__(root_src, root_dst)
self.recursive_archive_depth = 0
self.max_recursive_depth = max_recursive_depth
self.cur_file = None
self.logger = GroomerLogger(self.dst_root_path, debug)
def process_dir(self, src_dir, dst_dir):
"""Process a directory on the source key."""
self.logger.tree(src_dir)
for srcpath in self.list_all_files(src_dir):
dstpath = srcpath.replace(src_dir, dst_dir)
# TODO: Can we clean up the way we handle relative_path?
# Relative path is here so that when we print files in the log it
# shows only the file's path. Should we just pass it to the logger
# when we create it? Or let the logger figure it out?
# relative_path = srcpath.replace(src_dir + '/', '')
self.cur_file = File(srcpath, dstpath, self.logger)
self.process_file(self.cur_file)
def process_file(self, file):
"""
Process an individual file.
Check the file, handle archives using self.process_archive, copy
the file to the destionation key, and clean up temporary directory.
"""
file.check()
if file.is_recursive:
self.process_archive(file)
elif file.should_copy:
file.safe_copy()
file.set_property('copied', True)
file.write_log()
if hasattr(file, 'tempdir_path'):
self.safe_rmtree(file.tempdir_path)
def process_archive(self, file):
"""
Unpack an archive using 7zip and process contents using process_dir.
Should be given a Kittengroomer file object whose src_path points
to an archive.
"""
self.recursive_archive_depth += 1
if self.recursive_archive_depth >= self.max_recursive_depth:
file.make_dangerous('Archive bomb')
else:
tempdir_path = file.make_tempdir()
# TODO: double check we are properly escaping file.src_path
# otherwise we are running unvalidated user input directly in the shell
command_str = '{} -p1 x "{}" -o"{}" -bd -aoa'
unpack_command = command_str.format(SEVENZ_PATH,
file.src_path, tempdir_path)
self._run_process(unpack_command)
self.process_dir(tempdir_path, file.dst_path)
self.safe_rmtree(tempdir_path)
self.recursive_archive_depth -= 1
def _run_process(self, command_string, timeout=None):
"""Run command_string in a subprocess, wait until it finishes."""
args = shlex.split(command_string)
with open(self.logger.log_debug_err, 'ab') as stderr, open(self.logger.log_debug_out, 'ab') as stdout:
try:
subprocess.check_call(args, stdout=stdout, stderr=stderr, timeout=timeout)
except (subprocess.TimeoutExpired, subprocess.CalledProcessError):
return
return True
def run(self):
self.process_dir(self.src_root_path, self.dst_root_path)
def main(kg_implementation, description):
parser = argparse.ArgumentParser(prog='KittenGroomer', description=description)
parser.add_argument('-s', '--source', type=str, help='Source directory')
parser.add_argument('-d', '--destination', type=str, help='Destination directory')
args = parser.parse_args()
kg = kg_implementation(args.source, args.destination)
kg.run()
if __name__ == '__main__':
main(KittenGroomerFileCheck, 'File sanitizer used in CIRCLean. Renames potentially dangerous files.')
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