lib/pefile/peutils.py
# -*- coding: Latin-1 -*-
"""peutils, Portable Executable utilities module
Copyright (c) 2005-2011 Ero Carrera <ero.carrera@gmail.com>
All rights reserved.
For detailed copyright information see the file LICENSE in
the distribution archive.
"""
import os
import re
import string
import urllib
import pefile
__author__ = 'Ero Carrera'
__version__ = pefile.__version__
__contact__ = 'ero.carrera@gmail.com'
class SignatureDatabase:
"""This class loads and keeps a parsed PEiD signature database.
Usage:
sig_db = SignatureDatabase('/path/to/signature/file')
and/or
sig_db = SignatureDatabase()
sig_db.load('/path/to/signature/file')
Signature databases can be combined by performing multiple loads.
The filename parameter can be a URL too. In that case the
signature database will be downloaded from that location.
"""
def __init__(self, filename=None, data=None):
# RegExp to match a signature block
#
self.parse_sig = re.compile(
'\[(.*?)\]\s+?signature\s*=\s*(.*?)(\s+\?\?)*\s*ep_only\s*=\s*(\w+)(?:\s*section_start_only\s*=\s*(\w+)|)', re.S)
# Signature information
#
# Signatures are stored as trees using dictionaries
# The keys are the byte values while the values for
# each key are either:
#
# - Other dictionaries of the same form for further
# bytes in the signature
#
# - A dictionary with a string as a key (packer name)
# and None as value to indicate a full signature
#
self.signature_tree_eponly_true = dict ()
self.signature_count_eponly_true = 0
self.signature_tree_eponly_false = dict ()
self.signature_count_eponly_false = 0
self.signature_tree_section_start = dict ()
self.signature_count_section_start = 0
# The depth (length) of the longest signature
#
self.max_depth = 0
self.__load(filename=filename, data=data)
def generate_section_signatures(self, pe, name, sig_length=512):
"""Generates signatures for all the sections in a PE file.
If the section contains any data a signature will be created
for it. The signature name will be a combination of the
parameter 'name' and the section number and its name.
"""
section_signatures = list()
for idx, section in enumerate(pe.sections):
if section.SizeOfRawData < sig_length:
continue
#offset = pe.get_offset_from_rva(section.VirtualAddress)
offset = section.PointerToRawData
sig_name = '%s Section(%d/%d,%s)' % (
name, idx + 1, len(pe.sections),
''.join([c for c in section.Name if c in string.printable]))
section_signatures.append(
self.__generate_signature(
pe, offset, sig_name, ep_only=False,
section_start_only=True,
sig_length=sig_length) )
return '\n'.join(section_signatures)+'\n'
def generate_ep_signature(self, pe, name, sig_length=512):
"""Generate signatures for the entry point of a PE file.
Creates a signature whose name will be the parameter 'name'
and the section number and its name.
"""
offset = pe.get_offset_from_rva(pe.OPTIONAL_HEADER.AddressOfEntryPoint)
return self.__generate_signature(
pe, offset, name, ep_only=True, sig_length=sig_length)
def __generate_signature(self, pe, offset, name, ep_only=False,
section_start_only=False, sig_length=512):
data = pe.__data__[offset:offset+sig_length]
signature_bytes = ' '.join(['%02x' % ord(c) for c in data])
if ep_only == True:
ep_only = 'true'
else:
ep_only = 'false'
if section_start_only == True:
section_start_only = 'true'
else:
section_start_only = 'false'
signature = '[%s]\nsignature = %s\nep_only = %s\nsection_start_only = %s\n' % (
name, signature_bytes, ep_only, section_start_only)
return signature
def match(self, pe, ep_only=True, section_start_only=False):
"""Matches and returns the exact match(es).
If ep_only is True the result will be a string with
the packer name. Otherwise it will be a list of the
form (file_ofsset, packer_name). Specifying where
in the file the signature was found.
"""
matches = self.__match(pe, ep_only, section_start_only)
# The last match (the most precise) from the
# list of matches (if any) is returned
#
if matches:
if ep_only == False:
# Get the most exact match for each list of matches
# at a given offset
#
return [(match[0], match[1][-1]) for match in matches]
return matches[1][-1]
return None
def match_all(self, pe, ep_only=True, section_start_only=False):
"""Matches and returns all the likely matches."""
matches = self.__match(pe, ep_only, section_start_only)
if matches:
if ep_only == False:
# Get the most exact match for each list of matches
# at a given offset
#
return matches
return matches[1]
return None
def __match(self, pe, ep_only, section_start_only):
# Load the corresponding set of signatures
# Either the one for ep_only equal to True or
# to False
#
if section_start_only is True:
# Fetch the data of the executable as it'd
# look once loaded in memory
#
try :
data = pe.__data__
except Exception, excp :
raise
# Load the corresponding tree of signatures
#
signatures = self.signature_tree_section_start
# Set the starting address to start scanning from
#
scan_addresses = [section.PointerToRawData for section in pe.sections]
elif ep_only is True:
# Fetch the data of the executable as it'd
# look once loaded in memory
#
try :
data = pe.get_memory_mapped_image()
except Exception, excp :
raise
# Load the corresponding tree of signatures
#
signatures = self.signature_tree_eponly_true
# Fetch the entry point of the PE file and the data
# at the entry point
#
ep = pe.OPTIONAL_HEADER.AddressOfEntryPoint
# Set the starting address to start scanning from
#
scan_addresses = [ep]
else:
data = pe.__data__
signatures = self.signature_tree_eponly_false
scan_addresses = xrange( len(data) )
# For each start address, check if any signature matches
#
matches = []
for idx in scan_addresses:
result = self.__match_signature_tree(
signatures,
data[idx:idx+self.max_depth])
if result:
matches.append( (idx, result) )
# Return only the matched items found at the entry point if
# ep_only is True (matches will have only one element in that
# case)
#
if ep_only is True:
if matches:
return matches[0]
return matches
def match_data(self, code_data, ep_only=True, section_start_only=False):
data = code_data
scan_addresses = [ 0 ]
# Load the corresponding set of signatures
# Either the one for ep_only equal to True or
# to False
#
if section_start_only is True:
# Load the corresponding tree of signatures
#
signatures = self.signature_tree_section_start
# Set the starting address to start scanning from
#
elif ep_only is True:
# Load the corresponding tree of signatures
#
signatures = self.signature_tree_eponly_true
# For each start address, check if any signature matches
#
matches = []
for idx in scan_addresses:
result = self.__match_signature_tree(
signatures,
data[idx:idx+self.max_depth])
if result:
matches.append( (idx, result) )
# Return only the matched items found at the entry point if
# ep_only is True (matches will have only one element in that
# case)
#
if ep_only is True:
if matches:
return matches[0]
return matches
def __match_signature_tree(self, signature_tree, data, depth = 0):
"""Recursive function to find matches along the signature tree.
signature_tree is the part of the tree left to walk
data is the data being checked against the signature tree
depth keeps track of how far we have gone down the tree
"""
matched_names = list ()
match = signature_tree
# Walk the bytes in the data and match them
# against the signature
#
for idx, byte in enumerate ( [ord (b) for b in data] ):
# If the tree is exhausted...
#
if match is None :
break
# Get the next byte in the tree
#
match_next = match.get(byte, None)
# If None is among the values for the key
# it means that a signature in the database
# ends here and that there's an exact match.
#
if None in match.values():
# idx represent how deep we are in the tree
#
#names = [idx+depth]
names = list()
# For each of the item pairs we check
# if it has an element other than None,
# if not then we have an exact signature
#
for item in match.items():
if item[1] is None :
names.append (item[0])
matched_names.append(names)
# If a wildcard is found keep scanning the signature
# ignoring the byte.
#
if match.has_key ('??') :
match_tree_alternate = match.get ('??', None)
data_remaining = data[idx + 1 :]
if data_remaining:
matched_names.extend(
self.__match_signature_tree(
match_tree_alternate, data_remaining, idx+depth+1))
match = match_next
# If we have any more packer name in the end of the signature tree
# add them to the matches
#
if match is not None and None in match.values():
#names = [idx + depth + 1]
names = list()
for item in match.items() :
if item[1] is None:
names.append(item[0])
matched_names.append(names)
return matched_names
def load(self , filename=None, data=None):
"""Load a PEiD signature file.
Invoking this method on different files combines the signatures.
"""
self.__load(filename=filename, data=data)
def __load(self, filename=None, data=None):
if filename is not None:
# If the path does not exist, attempt to open a URL
#
if not os.path.exists(filename):
try:
sig_f = urllib.urlopen(filename)
sig_data = sig_f.read()
sig_f.close()
except IOError:
# Let this be raised back to the user...
raise
else:
# Get the data for a file
#
try:
sig_f = file( filename, 'rt' )
sig_data = sig_f.read()
sig_f.close()
except IOError:
# Let this be raised back to the user...
raise
else:
sig_data = data
# If the file/URL could not be read or no "raw" data
# was provided there's nothing else to do
#
if not sig_data:
return
# Helper function to parse the signature bytes
#
def to_byte(value) :
if value == '??' or value == '?0' :
return value
return int (value, 16)
# Parse all the signatures in the file
#
matches = self.parse_sig.findall(sig_data)
# For each signature, get the details and load it into the
# signature tree
#
for packer_name, signature, superfluous_wildcards, ep_only, section_start_only in matches:
ep_only = ep_only.strip().lower()
signature = signature.replace('\\n', '').strip()
signature_bytes = [to_byte(b) for b in signature.split()]
if ep_only == 'true':
ep_only = True
else:
ep_only = False
if section_start_only == 'true':
section_start_only = True
else:
section_start_only = False
depth = 0
if section_start_only is True:
tree = self.signature_tree_section_start
self.signature_count_section_start += 1
else:
if ep_only is True :
tree = self.signature_tree_eponly_true
self.signature_count_eponly_true += 1
else :
tree = self.signature_tree_eponly_false
self.signature_count_eponly_false += 1
for idx, byte in enumerate (signature_bytes) :
if idx+1 == len(signature_bytes):
tree[byte] = tree.get( byte, dict() )
tree[byte][packer_name] = None
else :
tree[byte] = tree.get ( byte, dict() )
tree = tree[byte]
depth += 1
if depth > self.max_depth:
self.max_depth = depth
def is_valid( pe ):
""""""
pass
def is_suspicious( pe ):
"""
unusual locations of import tables
non recognized section names
presence of long ASCII strings
"""
relocations_overlap_entry_point = False
sequential_relocs = 0
# If relocation data is found and the entries go over the entry point, and also are very
# continuous or point outside section's boundaries => it might imply that an obfuscation
# trick is being used or the relocations are corrupt (maybe intentionally)
#
if hasattr(pe, 'DIRECTORY_ENTRY_BASERELOC'):
for base_reloc in pe.DIRECTORY_ENTRY_BASERELOC:
last_reloc_rva = None
for reloc in base_reloc.entries:
if reloc.rva <= pe.OPTIONAL_HEADER.AddressOfEntryPoint <= reloc.rva + 4:
relocations_overlap_entry_point = True
if last_reloc_rva is not None and last_reloc_rva <= reloc.rva <= last_reloc_rva + 4:
sequential_relocs += 1
last_reloc_rva = reloc.rva
# If import tables or strings exist (are pointed to) to within the header or in the area
# between the PE header and the first section that's supicious
#
# IMPLEMENT
warnings_while_parsing = False
# If we have warnings, that's suspicious, some of those will be because of out-of-ordinary
# values are found in the PE header fields
# Things that are reported in warnings:
# (parsing problems, special section characteristics i.e. W & X, uncommon values of fields,
# unusual entrypoint, suspicious imports)
#
warnings = pe.get_warnings()
if warnings:
warnings_while_parsing
# If there are few or none (should come with a standard "density" of strings/kilobytes of data) longer (>8)
# ascii sequences that might indicate packed data, (this is similar to the entropy test in some ways but
# might help to discard cases of legitimate installer or compressed data)
# If compressed data (high entropy) and is_driver => uuuuhhh, nasty
pass
def is_probably_packed( pe ):
"""Returns True is there is a high likelihood that a file is packed or contains compressed data.
The sections of the PE file will be analyzed, if enough sections
look like containing containing compressed data and the data makes
up for more than 20% of the total file size. The function will
return True.
"""
# Calculate the lenth of the data up to the end of the last section in the
# file. Overlay data won't be taken into account
#
total_pe_data_length = len( pe.trim() )
has_significant_amount_of_compressed_data = False
# If some of the sections have high entropy and they make for more than 20% of the file's size
# it's assumed that it could be an installer or a packed file
total_compressed_data = 0
for section in pe.sections:
s_entropy = section.get_entropy()
s_length = len( section.get_data() )
# The value of 7.4 is empircal, based of looking at a few files packed
# by different packers
if s_entropy > 7.4:
total_compressed_data += s_length
if ((1.0 * total_compressed_data)/total_pe_data_length) > .2:
has_significant_amount_of_compressed_data = True
return has_significant_amount_of_compressed_data