Merge pull request #317 from samiraguiar/oleobj-detect-external

oleobj: detect external links

Merge pull request #317 from samiraguiar/oleobj-detect-external
oleobj: detect external links
Philippe Lagadec · GitHub
2 parents d3b8857d a5ac0720
Showing 16 changed files with 105 additions and 24 deletions
oletools/oleobj.py
oletools/ooxml.py
tests/oleobj/test_external_links.py
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.docm
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.docx
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.dotm
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.dotx
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.potm
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.potx
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.ppsm
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.ppsx
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.pptm
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.pptx
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.xlsb
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.xlsm
tests/test-data/oleobj/external_link/sample_with_external_link_to_doc.xlsx
@@ -50,7 +50,7 @@ import os
 import re
 import sys
 import io
-from zipfile import is_zipfile, ZipFile
+from zipfile import is_zipfile
  
 import olefile
  
@@ -72,7 +72,7 @@ except ImportError:
  
 from oletools.ppt_record_parser import (is_ppt, PptFile,
                                         PptRecordExOleVbaActiveXAtom)
-from oletools.ooxml import ZipSubFile
+from oletools.ooxml import XmlParser
  
 # -----------------------------------------------------------------------------
 # CHANGELOG:
@@ -181,6 +181,7 @@ else:
     NULL_CHAR = 0     # pylint: disable=redefined-variable-type
     xrange = range    # pylint: disable=redefined-builtin, invalid-name
  
+OOXML_RELATIONSHIP_TAG = '{http://schemas.openxmlformats.org/package/2006/relationships}Relationship'
  
 # === GLOBAL VARIABLES ========================================================
  
@@ -206,6 +207,24 @@ RETURN_ERR_ARGS = 2    # reserve for OptionParser.parse_args
 RETURN_ERR_STREAM = 4  # error opening/parsing a stream
 RETURN_ERR_DUMP = 8    # error dumping data from stream to file
  
+# Not sure if they can all be "External", but just in case
+BLACKLISTED_RELATIONSHIP_TYPES = [
+    'attachedTemplate',
+    'externalLink',
+    'externalLinkPath',
+    'externalReference'
+    'frame'
+    'hyperlink',
+    'officeDocument',
+    'oleObject',
+    'package',
+    'slideUpdateUrl',
+    'slideMaster',
+    'slide',
+    'slideUpdateInfo',
+    'subDocument',
+    'worksheet'
+]
  
 # === FUNCTIONS ===============================================================
  
@@ -599,7 +618,7 @@ class FakeFile(io.RawIOBase):
         return self.pos
  
  
-def find_ole(filename, data):
+def find_ole(filename, data, xml_parser=None):
     """ try to open somehow as zip/ole/rtf/... ; yield None if fail
  
     If data is given, filename is (mostly) ignored.
@@ -631,34 +650,40 @@ def find_ole(filename, data):
             log.info('is ole file: ' + filename)
             ole = olefile.OleFileIO(arg_for_ole)
             yield ole
-        elif is_zipfile(arg_for_zip):
+        elif xml_parser is not None or is_zipfile(arg_for_zip):
+            # keep compatibility with 3rd-party code that calls this function
+            # directly without providing an XmlParser instance
+            if xml_parser is None:
+                xml_parser = XmlParser(arg_for_zip)
+                # force iteration so XmlParser.iter_non_xml() returns data
+                [x for x in xml_parser.iter_xml()]
+
             log.info('is zip file: ' + filename)
-            zipper = ZipFile(arg_for_zip, 'r')
-            for subfile in zipper.namelist():
-                head = b''
+            # we looped through the XML files before, now we can
+            # iterate the non-XML files looking for ole objects
+            for subfile, _, file_handle in xml_parser.iter_non_xml():
                 try:
-                    with zipper.open(subfile) as file_handle:
-                        head = file_handle.read(len(olefile.MAGIC))
+                    head = file_handle.read(len(olefile.MAGIC))
                 except RuntimeError:
                     log.error('zip is encrypted: ' + filename)
                     yield None
                     continue
  
                 if head == olefile.MAGIC:
+                    file_handle.seek(0)
                     log.info('  unzipping ole: ' + subfile)
-                    with ZipSubFile(zipper, subfile) as file_handle:
-                        try:
-                            ole = olefile.OleFileIO(file_handle)
-                            yield ole
-                        except IOError:
-                            log.warning('Error reading data from {0}/{1} or '
-                                        'interpreting it as OLE object'
-                                        .format(filename, subfile))
-                            log.debug('', exc_info=True)
-                        finally:
-                            if ole is not None:
-                                ole.close()
-                                ole = None
+                    try:
+                        ole = olefile.OleFileIO(file_handle)
+                        yield ole
+                    except IOError:
+                        log.warning('Error reading data from {0}/{1} or '
+                                    'interpreting it as OLE object'
+                                    .format(filename, subfile))
+                        log.debug('', exc_info=True)
+                    finally:
+                        if ole is not None:
+                            ole.close()
+                            ole = None
                 else:
                     log.debug('unzip skip: ' + subfile)
         else:
@@ -674,6 +699,22 @@ def find_ole(filename, data):
             ole.close()
  
  
+def find_external_relationships(xml_parser):
+    """ iterate XML files looking for relationships to external objects
+    """
+    for _, elem, _ in xml_parser.iter_xml(None, False, OOXML_RELATIONSHIP_TAG):
+        try:
+            if elem.attrib['TargetMode'] == 'External':
+                relationship_type = elem.attrib['Type'].rsplit('/', 1)[1]
+
+                if relationship_type in BLACKLISTED_RELATIONSHIP_TYPES:
+                    yield relationship_type, elem.attrib['Target']
+        except (AttributeError, KeyError):
+            # ignore missing attributes - Word won't detect
+            # external links anyway
+            pass
+
+
 def process_file(filename, data, output_dir=None):
     """ find embedded objects in given file
  
@@ -706,10 +747,19 @@ def process_file(filename, data, output_dir=None):
     err_dumping = False
     did_dump = False
  
+    xml_parser = None
+    if is_zipfile(filename):
+        log.info('file is a OOXML file, looking for relationships with external links')
+        xml_parser = XmlParser(filename)
+        for relationship, target in find_external_relationships(xml_parser):
+            did_dump = True
+            print("Found relationship '%s' with external link %s" % (relationship, target))
+
+
     # look for ole files inside file (e.g. unzip docx)
     # have to finish work on every ole stream inside iteration, since handles
     # are closed in find_ole
-    for ole in find_ole(filename, data):
+    for ole in find_ole(filename, data, xml_parser):
         if ole is None:    # no ole file found
             continue
  
@@ -644,7 +644,7 @@ def test():
     for subfile, elem, depth in parser.iter_xml():
         if depth < 4:
             print(u'{0} {1}{2}'.format(subfile, '  ' * depth, debug_str(elem)))
-    for index, (subfile, content_type) in enumerate(parser.iter_non_xml()):
+    for index, (subfile, content_type, _) in enumerate(parser.iter_non_xml()):
         print(u'Non-XML subfile: {0} of type {1}'
               .format(subfile, content_type or u'unknown'))
         if index > 100:
+""" Test that oleobj detects external links in relationships files.
+"""
+
+import unittest
+import os
+from os import path
+
+# Directory with test data, independent of current working directory
+from tests.test_utils import DATA_BASE_DIR
+from oletools import oleobj
+
+BASE_DIR = path.join(DATA_BASE_DIR, 'oleobj', 'external_link')
+
+
+class TestExternalLinks(unittest.TestCase):
+    def test_external_links(self):
+        """
+        loop through sample files asserting that external links are found
+        """
+
+        for dirpath, _, filenames in os.walk(BASE_DIR):
+            for filename in filenames:
+                file_path = path.join(dirpath, filename)
+
+                ret_val = oleobj.main([file_path])
+                self.assertEqual(ret_val, oleobj.RETURN_DID_DUMP)
+
+
+# just in case somebody calls this file as a script
+if __name__ == '__main__':
+    unittest.main()