Handle malformed AndroidQF backups (#824)

src/mvt/android/cmd_check_androidqf.py

@@ -13,7 +13,7 @@ from typing import List, Optional
 
 from mvt.android.artifacts.getprop import GetProp
 from mvt.android.cmd_check_intrusion_logs import CmdAndroidCheckIntrusionLogs
-from mvt.android.cmd_check_backup import CmdAndroidCheckBackup
+from mvt.android.cmd_check_backup import CmdAndroidCheckBackup, InvalidAndroidBackup
 from mvt.android.cmd_check_bugreport import CmdAndroidCheckBugreport
 from mvt.common.command import Command
 from mvt.common.indicators import Indicators
@@ -240,7 +240,14 @@ class CmdAndroidCheckAndroidQF(Command):
             hashes=self.hashes,
             sub_command=True,
         )
-        cmd.from_ab(backup)
+        try:
+            cmd.from_ab(backup)
+        except InvalidAndroidBackup as exc:
+            self.log.warning(
+                "Skipping backup modules as backup.ab is malformed: %s", exc
+            )
+            return False
+
         cmd.run()
 
         self.timeline.extend(cmd.timeline)

src/mvt/android/cmd_check_backup.py

@@ -27,6 +27,10 @@ from .modules.backup import BACKUP_MODULES
 log = logging.getLogger(__name__)
 
 
+class InvalidAndroidBackup(Exception):
+    pass
+
+
 class CmdAndroidCheckBackup(Command):
     def __init__(
         self,
@@ -68,6 +72,10 @@ class CmdAndroidCheckBackup(Command):
         self.__type = "ab"
         header = parse_ab_header(ab_file_bytes)
         if not header["backup"]:
+            if self.sub_command:
+                raise InvalidAndroidBackup(
+                    "Invalid backup format, file should be in .ab format"
+                )
             log.critical("Invalid backup format, file should be in .ab format")
             sys.exit(1)
 
@@ -83,12 +91,25 @@ class CmdAndroidCheckBackup(Command):
             log.critical("Invalid backup password")
             sys.exit(1)
         except AndroidBackupParsingError as exc:
+            if self.sub_command:
+                raise InvalidAndroidBackup(
+                    f"Impossible to parse this backup file: {exc}"
+                ) from exc
             log.critical("Impossible to parse this backup file: %s", exc)
             log.critical("Please use Android Backup Extractor (ABE) instead")
             sys.exit(1)
 
         dbytes = io.BytesIO(tardata)
-        self.__tar = tarfile.open(fileobj=dbytes)
+        try:
+            self.__tar = tarfile.open(fileobj=dbytes)
+        except tarfile.TarError as exc:
+            if self.sub_command:
+                raise InvalidAndroidBackup(
+                    f"Impossible to parse this backup file: {exc}"
+                ) from exc
+            log.critical("Impossible to parse this backup file: %s", exc)
+            log.critical("Please use Android Backup Extractor (ABE) instead")
+            sys.exit(1)
         for member in self.__tar:
             self.__files.append(member.name)
 

src/mvt/android/modules/androidqf/sms.py

@@ -58,7 +58,7 @@ class SMS(AndroidQFModule):
     def parse_backup(self, data):
         header = parse_ab_header(data)
         if not header["backup"]:
-            self.log.critical("Invalid backup format, backup.ab was not analysed")
+            self.log.warning("Invalid backup format, backup.ab was not analysed")
             return
 
         password = None
@@ -76,7 +76,7 @@ class SMS(AndroidQFModule):
             self.log.critical("Invalid backup password")
             return
         except AndroidBackupParsingError:
-            self.log.critical(
+            self.log.warning(
                 "Impossible to parse this backup file, please use"
                 " Android Backup Extractor instead"
             )

src/mvt/android/parsers/backup.py

@@ -48,13 +48,16 @@ def parse_ab_header(data):
         'encryption': "none", 'version': 4}
     """
     if data.startswith(b"ANDROID BACKUP"):
-        [_, version, is_compressed, encryption, _] = data.split(b"\n", 4)
-        return {
-            "backup": True,
-            "compression": (is_compressed == b"1"),
-            "version": int(version),
-            "encryption": encryption.decode("utf-8"),
-        }
+        try:
+            [_, version, is_compressed, encryption, _] = data.split(b"\n", 4)
+            return {
+                "backup": True,
+                "compression": (is_compressed == b"1"),
+                "version": int(version),
+                "encryption": encryption.decode("utf-8"),
+            }
+        except (UnicodeDecodeError, ValueError):
+            pass
 
     return {"backup": False, "compression": None, "version": None, "encryption": None}
 

tests/android/test_backup_parser.py

@@ -5,12 +5,24 @@
 
 import hashlib
 
-from mvt.android.parsers.backup import parse_backup_file, parse_tar_for_sms
+from mvt.android.parsers.backup import (
+    parse_ab_header,
+    parse_backup_file,
+    parse_tar_for_sms,
+)
 
 from ..utils import get_artifact
 
 
 class TestBackupParsing:
+    def test_parse_incomplete_header(self):
+        assert parse_ab_header(b"ANDROID BACKUP\n") == {
+            "backup": False,
+            "compression": None,
+            "version": None,
+            "encryption": None,
+        }
+
     def test_parsing_noencryption(self):
         file = get_artifact("android_backup/backup.ab")
         with open(file, "rb") as f:

tests/test_check_android_androidqf.py

@@ -3,7 +3,9 @@
 # Use of this software is governed by the MVT License 1.1 that can be found at
 #   https://license.mvt.re/1.1/
 
+import logging
 import os
+import shutil
 
 from click.testing import CliRunner
 
@@ -68,3 +70,18 @@ class TestCheckAndroidqfCommand:
         assert result.exit_code == 0
         del os.environ["MVT_ANDROID_BACKUP_PASSWORD"]
         settings.__init__()  # Reset settings
+
+    def test_check_malformed_backup_skips_backup_modules(self, tmp_path, caplog):
+        path = tmp_path / "androidqf"
+        shutil.copytree(os.path.join(get_artifact_folder(), "androidqf"), path)
+        (path / "backup.ab").write_bytes(b"")
+
+        runner = CliRunner()
+        with caplog.at_level(logging.WARNING):
+            result = runner.invoke(check_androidqf, [str(path)])
+
+        assert result.exit_code == 0
+        assert "Skipping backup modules as backup.ab is malformed" in caplog.text
+        assert not any(
+            record.levelname in {"CRITICAL", "FATAL"} for record in caplog.records
+        )