Merge c85000591b into 37cea84f77

* from https://github.com/yt-dlp/yt-dlp/security/advisories/GHSA-79w7-vh3h-8g4, thx grub4k

test/test_utils.py

@@ -14,9 +14,11 @@ sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 import io
 import itertools
 import json
+import types
 import xml.etree.ElementTree
 
 from youtube_dl.utils import (
+    _UnsafeExtensionError,
     age_restricted,
     args_to_str,
     base_url,
@@ -270,6 +272,27 @@ class TestUtil(unittest.TestCase):
             expand_path('~/%s' % env('YOUTUBE_DL_EXPATH_PATH')),
             '%s/expanded' % compat_getenv('HOME'))
 
+    _uncommon_extensions = [
+        ('exe', 'abc.exe.ext'),
+        ('de', 'abc.de.ext'),
+        ('../.mp4', None),
+        ('..\\.mp4', None),
+    ]
+
+    def assertUnsafeExtension(self, ext=None):
+        assert_raises = self.assertRaises(_UnsafeExtensionError)
+        assert_raises.ext = ext
+        orig_exit = assert_raises.__exit__
+
+        def my_exit(self_, exc_type, exc_val, exc_tb):
+            did_raise = orig_exit(exc_type, exc_val, exc_tb)
+            if did_raise and assert_raises.ext is not None:
+                self.assertEqual(assert_raises.ext, assert_raises.exception.extension, 'Unsafe extension  not as unexpected')
+            return did_raise
+
+        assert_raises.__exit__ = types.MethodType(my_exit, assert_raises)
+        return assert_raises
+
     def test_prepend_extension(self):
         self.assertEqual(prepend_extension('abc.ext', 'temp'), 'abc.temp.ext')
         self.assertEqual(prepend_extension('abc.ext', 'temp', 'ext'), 'abc.temp.ext')
@@ -278,6 +301,19 @@ class TestUtil(unittest.TestCase):
         self.assertEqual(prepend_extension('.abc', 'temp'), '.abc.temp')
         self.assertEqual(prepend_extension('.abc.ext', 'temp'), '.abc.temp.ext')
 
+        # Test uncommon extensions
+        self.assertEqual(prepend_extension('abc.ext', 'bin'), 'abc.bin.ext')
+        for ext, result in self._uncommon_extensions:
+            with self.assertUnsafeExtension(ext):
+                prepend_extension('abc', ext)
+            if result:
+                self.assertEqual(prepend_extension('abc.ext', ext, 'ext'), result)
+            else:
+                with self.assertUnsafeExtension(ext):
+                    prepend_extension('abc.ext', ext, 'ext')
+            with self.assertUnsafeExtension(ext):
+                prepend_extension('abc.unexpected_ext', ext, 'ext')
+
     def test_replace_extension(self):
         self.assertEqual(replace_extension('abc.ext', 'temp'), 'abc.temp')
         self.assertEqual(replace_extension('abc.ext', 'temp', 'ext'), 'abc.temp')
@@ -286,6 +322,16 @@ class TestUtil(unittest.TestCase):
         self.assertEqual(replace_extension('.abc', 'temp'), '.abc.temp')
         self.assertEqual(replace_extension('.abc.ext', 'temp'), '.abc.temp')
 
+        # Test uncommon extensions
+        self.assertEqual(replace_extension('abc.ext', 'bin'), 'abc.unknown_video')
+        for ext, _ in self._uncommon_extensions:
+            with self.assertUnsafeExtension(ext):
+                replace_extension('abc', ext)
+            with self.assertUnsafeExtension(ext):
+                replace_extension('abc.ext', ext, 'ext')
+            with self.assertUnsafeExtension(ext):
+                replace_extension('abc.unexpected_ext', ext, 'ext')
+
     def test_subtitles_filename(self):
         self.assertEqual(subtitles_filename('abc.ext', 'en', 'vtt'), 'abc.en.vtt')
         self.assertEqual(subtitles_filename('abc.ext', 'en', 'vtt', 'ext'), 'abc.en.vtt')

youtube_dl/YoutubeDL.py

@@ -7,6 +7,7 @@ import collections
 import copy
 import datetime
 import errno
+import functools
 import io
 import itertools
 import json
@@ -53,6 +54,7 @@ from .compat import (
     compat_urllib_request_DataHandler,
 )
 from .utils import (
+    _UnsafeExtensionError,
     age_restricted,
     args_to_str,
     bug_reports_message,
@@ -129,6 +131,20 @@ if compat_os_name == 'nt':
     import ctypes
 
 
+def _catch_unsafe_file_extension(func):
+    @functools.wraps(func)
+    def wrapper(self, *args, **kwargs):
+        try:
+            return func(self, *args, **kwargs)
+        except _UnsafeExtensionError as error:
+            self.report_error(
+                '{0} found; to avoid damaging your system, this value is disallowed.'
+                ' If you believe this is an error{1}').format(
+                    error.message, bug_reports_message(','))
+
+    return wrapper
+
+
 class YoutubeDL(object):
     """YoutubeDL class.
 
@@ -1925,6 +1941,7 @@ class YoutubeDL(object):
         if self.params.get('forcejson', False):
             self.to_stdout(json.dumps(self.sanitize_info(info_dict)))
 
+    @_catch_unsafe_file_extension
     def process_info(self, info_dict):
         """Process a single resolved IE result."""
 
@@ -2371,60 +2388,38 @@ class YoutubeDL(object):
         return res
 
     def _format_note(self, fdict):
-        res = ''
-        if fdict.get('ext') in ['f4f', 'f4m']:
-            res += '(unsupported) '
+        note_parts = []
+        if fdict.get('ext') in ('f4f', 'f4m'):
+            note_parts.append('(unsupported)')
         if fdict.get('language'):
-            if res:
-                res += ' '
-            res += '[%s] ' % fdict['language']
-        if fdict.get('format_note') is not None:
-            res += fdict['format_note'] + ' '
+            note_parts.append(f'[{fdict["language"]}]')
+        if fdict.get('format_note'):
+            note_parts.append(fdict['format_note'])
         if fdict.get('tbr') is not None:
-            res += '%4dk ' % fdict['tbr']
+            note_parts.append('%4dk' % fdict['tbr'])
         if fdict.get('container') is not None:
-            if res:
-                res += ', '
-            res += '%s container' % fdict['container']
-        if (fdict.get('vcodec') is not None
-                and fdict.get('vcodec') != 'none'):
-            if res:
-                res += ', '
-            res += fdict['vcodec']
-            if fdict.get('vbr') is not None:
-                res += '@'
-        elif fdict.get('vbr') is not None and fdict.get('abr') is not None:
-            res += 'video@'
+            note_parts.append('%s container' % fdict['container'])
+        if fdict.get('vcodec') not in (None, 'none'):
+            note_parts.append(fdict['vcodec'] + ('@' if fdict.get('vbr') else ''))
+        elif fdict.get('vbr') is not None:
+            note_parts.append('video@')
         if fdict.get('vbr') is not None:
-            res += '%4dk' % fdict['vbr']
+            note_parts.append('%4dk' % fdict['vbr'])
         if fdict.get('fps') is not None:
-            if res:
-                res += ', '
-            res += '%sfps' % fdict['fps']
+            note_parts.append('%sfps' % fdict['fps'])
         if fdict.get('acodec') is not None:
-            if res:
-                res += ', '
-            if fdict['acodec'] == 'none':
-                res += 'video only'
-            else:
-                res += '%-5s' % fdict['acodec']
+            note_parts.append('video only' if fdict['acodec'] == 'none' else '%-5s' % fdict['acodec'])
         elif fdict.get('abr') is not None:
-            if res:
-                res += ', '
-            res += 'audio'
+            note_parts.append('audio')
         if fdict.get('abr') is not None:
-            res += '@%3dk' % fdict['abr']
+            note_parts.append('@%3dk' % fdict['abr'])
         if fdict.get('asr') is not None:
-            res += ' (%5dHz)' % fdict['asr']
+            note_parts.append('(%5dHz)' % fdict['asr'])
         if fdict.get('filesize') is not None:
-            if res:
-                res += ', '
-            res += format_bytes(fdict['filesize'])
+            note_parts.append(format_bytes(fdict['filesize']))
         elif fdict.get('filesize_approx') is not None:
-            if res:
-                res += ', '
-            res += '~' + format_bytes(fdict['filesize_approx'])
-        return res
+            note_parts.append('~' + format_bytes(fdict['filesize_approx']))
+        return ' '.join(note_parts)
 
     def list_formats(self, info_dict):
         formats = info_dict.get('formats', [info_dict])

youtube_dl/__init__.py

@@ -21,6 +21,7 @@ from .compat import (
     workaround_optparse_bug9161,
 )
 from .utils import (
+    _UnsafeExtensionError,
     DateRange,
     decodeOption,
     DEFAULT_OUTTMPL,
@@ -173,6 +174,9 @@ def _real_main(argv=None):
     if opts.ap_mso and opts.ap_mso not in MSO_INFO:
         parser.error('Unsupported TV Provider, use --ap-list-mso to get a list of supported TV Providers')
 
+    if opts.no_check_extensions:
+        _UnsafeExtensionError.lenient = True
+
     def parse_retries(retries):
         if retries in ('inf', 'infinite'):
             parsed_retries = float('inf')

youtube_dl/extractor/youtube.py

@@ -87,6 +87,7 @@ class YoutubeBaseInfoExtractor(InfoExtractor):
         If _LOGIN_REQUIRED is set and no authentication was provided, an error is raised.
         """
         username, password = self._get_login_info()
+
         # No authentication to be performed
         if username is None:
             if self._LOGIN_REQUIRED and self._downloader.params.get('cookiefile') is None:
@@ -129,21 +130,20 @@ class YoutubeBaseInfoExtractor(InfoExtractor):
             self._downloader.report_warning(message)
 
         lookup_req = [
-            username,
-            None, [], None, 'US', None, None, 2, False, True,
-            [
-                None, None,
-                [2, 1, None, 1,
-                 'https://accounts.google.com/ServiceLogin?passive=true&continue=https%3A%2F%2Fwww.youtube.com%2Fsignin%3Fnext%3D%252F%26action_handle_signin%3Dtrue%26hl%3Den%26app%3Ddesktop%26feature%3Dsign_in_button&hl=en&service=youtube&uilel=3&requestPath=%2FServiceLogin&Page=PasswordSeparationSignIn',
-                 None, [], 4],
-                1, [None, None, []], None, None, None, True
-            ],
+            username, None, [], None, 'US', None, None, 2, False, True,
+            [None, None, [2, 1, None, 1,
+                          'https://accounts.google.com/ServiceLogin?passive=true&continue=https%3A%2F%2Fwww.youtube.com%2Fsignin%3Fnext%3D%252F%26action_handle_signin%3Dtrue%26hl%3Den%26app%3Ddesktop%26feature%3Dsign_in_button&hl=en&service=youtube&uilel=3&requestPath=%2FServiceLogin&Page=PasswordSeparationSignIn',
+                          None, [], 4], 1, [None, None, []], None, None, None, True],
             username,
         ]
 
-        lookup_results = req(
-            self._LOOKUP_URL, lookup_req,
-            'Looking up account info', 'Unable to look up account info')
+        # --- Cambio 1: Extracción de función para mejorar la legibilidad ---
+        def perform_lookup(req):
+            return self._download_json(
+                self._LOOKUP_URL, req,
+                'Looking up account info', 'Unable to look up account info')
+
+        lookup_results = perform_lookup(lookup_req)
 
         if lookup_results is False:
             return False
@@ -154,12 +154,10 @@ class YoutubeBaseInfoExtractor(InfoExtractor):
             return False
 
         challenge_req = [
-            user_hash,
-            None, 1, None, [1, None, None, None, [password, None, True]],
-            [
-                None, None, [2, 1, None, 1, 'https://accounts.google.com/ServiceLogin?passive=true&continue=https%3A%2F%2Fwww.youtube.com%2Fsignin%3Fnext%3D%252F%26action_handle_signin%3Dtrue%26hl%3Den%26app%3Ddesktop%26feature%3Dsign_in_button&hl=en&service=youtube&uilel=3&requestPath=%2FServiceLogin&Page=PasswordSeparationSignIn', None, [], 4],
-                1, [None, None, []], None, None, None, True
-            ]]
+            user_hash, None, 1, None, [1, None, None, None, [password, None, True]],
+            [None, None, [2, 1, None, 1,
+                          'https://accounts.google.com/ServiceLogin?passive=true&continue=https%3A%2F%2Fwww.youtube.com%2Fsignin%3Fnext%3D%252F%26action_handle_signin%3Dtrue%26hl%3Den%26app%3Ddesktop%26feature%3Dsign_in_button&hl=en&service=youtube&uilel=3&requestPath=%2FServiceLogin&Page=PasswordSeparationSignIn',
+                          None, [], 4], 1, [None, None, []], None, None, None, True]]
 
         challenge_results = req(
             self._CHALLENGE_URL, challenge_req,

youtube_dl/options.py

@@ -533,6 +533,10 @@ def parseOpts(overrideArguments=None):
         '--no-check-certificate',
         action='store_true', dest='no_check_certificate', default=False,
         help='Suppress HTTPS certificate validation')
+    workarounds.add_option(
+        '--no-check-extensions',
+        action='store_true', dest='no_check_extensions', default=False,
+        help='Suppress file extension validation')
     workarounds.add_option(
         '--prefer-insecure',
         '--prefer-unsecure', action='store_true', dest='prefer_insecure',

youtube_dl/utils.py

@@ -1717,21 +1717,6 @@ TIMEZONE_NAMES = {
     'PST': -8, 'PDT': -7   # Pacific
 }
 
-KNOWN_EXTENSIONS = (
-    'mp4', 'm4a', 'm4p', 'm4b', 'm4r', 'm4v', 'aac',
-    'flv', 'f4v', 'f4a', 'f4b',
-    'webm', 'ogg', 'ogv', 'oga', 'ogx', 'spx', 'opus',
-    'mkv', 'mka', 'mk3d',
-    'avi', 'divx',
-    'mov',
-    'asf', 'wmv', 'wma',
-    '3gp', '3g2',
-    'mp3',
-    'flac',
-    'ape',
-    'wav',
-    'f4f', 'f4m', 'm3u8', 'smil')
-
 # needed for sanitizing filenames in restricted mode
 ACCENT_CHARS = dict(zip('ÂÃÄÀÁÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖŐØŒÙÚÛÜŰÝÞßàáâãäåæçèéêëìíîïðñòóôõöőøœùúûüűýþÿ',
                         itertools.chain('AAAAAA', ['AE'], 'CEEEEIIIIDNOOOOOOO', ['OE'], 'UUUUUY', ['TH', 'ss'],
@@ -3959,19 +3944,22 @@ def parse_duration(s):
     return duration
 
 
-def prepend_extension(filename, ext, expected_real_ext=None):
+def _change_extension(prepend, filename, ext, expected_real_ext=None):
     name, real_ext = os.path.splitext(filename)
-    return (
-        '{0}.{1}{2}'.format(name, ext, real_ext)
-        if not expected_real_ext or real_ext[1:] == expected_real_ext
-        else '{0}.{1}'.format(filename, ext))
+    sanitize_extension = _UnsafeExtensionError.sanitize_extension
+
+    if not expected_real_ext or real_ext.partition('.')[0::2] == ('', expected_real_ext):
+        filename = name
+        if prepend and real_ext:
+            sanitize_extension(ext, prepend=prepend)
+            return ''.join((filename, '.', ext, real_ext))
+
+    # Mitigate path traversal and file impersonation attacks
+    return '.'.join((filename, sanitize_extension(ext)))
 
 
-def replace_extension(filename, ext, expected_real_ext=None):
-    name, real_ext = os.path.splitext(filename)
-    return '{0}.{1}'.format(
-        name if not expected_real_ext or real_ext[1:] == expected_real_ext else filename,
-        ext)
+prepend_extension = functools.partial(_change_extension, True)
+replace_extension = functools.partial(_change_extension, False)
 
 
 def check_executable(exe, args=[]):
@@ -6002,114 +5990,63 @@ def parse_m3u8_attributes(attrib):
 def urshift(val, n):
     return val >> n if val >= 0 else (val + 0x100000000) >> n
 
-
 # Based on png2str() written by @gdkchan and improved by @yokrysty
 # Originally posted at https://github.com/ytdl-org/youtube-dl/issues/9706
 def decode_png(png_data):
     # Reference: https://www.w3.org/TR/PNG/
-    header = png_data[8:]
-
-    if png_data[:8] != b'\x89PNG\x0d\x0a\x1a\x0a' or header[4:8] != b'IHDR':
+    if png_data[:8] != b'\x89PNG\x0d\x0a\x1a\x0a':
         raise IOError('Not a valid PNG file.')
 
-    int_map = {1: '>B', 2: '>H', 4: '>I'}
-    unpack_integer = lambda x: compat_struct_unpack(int_map[len(x)], x)[0]
+    def unpack_integer(data):
+        return compat_struct_unpack(f'>{int_map[len(data)]}', data)[0]
 
+    int_map = {1: 'B', 2: 'H', 4: 'I'}
+    header = png_data[8:]
     chunks = []
 
     while header:
         length = unpack_integer(header[:4])
-        header = header[4:]
+        chunk_type, chunk_data, header = header[4:8], header[8:8 + length], header[8 + length + 4:]
+        chunks.append({'type': chunk_type, 'data': chunk_data})
 
-        chunk_type = header[:4]
-        header = header[4:]
+    if not (ihdr := next((c["data"] for c in chunks if c["type"] == b'IHDR'), None)):
+        raise IOError("Unable to read PNG header.")
 
-        chunk_data = header[:length]
-        header = header[length:]
-
-        header = header[4:]  # Skip CRC
-
-        chunks.append({
-            'type': chunk_type,
-            'length': length,
-            'data': chunk_data
-        })
-
-    ihdr = chunks[0]['data']
-
-    width = unpack_integer(ihdr[:4])
-    height = unpack_integer(ihdr[4:8])
-
-    idat = b''
-
-    for chunk in chunks:
-        if chunk['type'] == b'IDAT':
-            idat += chunk['data']
+    width, height = unpack_integer(ihdr[:4]), unpack_integer(ihdr[4:8])
+    idat = b''.join(c['data'] for c in chunks if c['type'] == b'IDAT')
 
     if not idat:
         raise IOError('Unable to read PNG data.')
 
     decompressed_data = bytearray(zlib.decompress(idat))
-
     stride = width * 3
-    pixels = []
-
-    def _get_pixel(idx):
-        x = idx % stride
-        y = idx // stride
-        return pixels[y][x]
+    pixels = [[] for _ in range(height)]
+    
+    def _get_pixel(x, y):
+        return pixels[y][x] if x >= 0 and y >= 0 else 0
 
     for y in range(height):
-        basePos = y * (1 + stride)
-        filter_type = decompressed_data[basePos]
-
-        current_row = []
-
-        pixels.append(current_row)
-
+        filter_type = decompressed_data[y * (1 + stride)]
         for x in range(stride):
-            color = decompressed_data[1 + basePos + x]
-            basex = y * stride + x
-            left = 0
-            up = 0
+            color = decompressed_data[1 + y * (1 + stride) + x]
+            left, up = _get_pixel(x - 3, y), _get_pixel(x, y - 1)
 
-            if x > 2:
-                left = _get_pixel(basex - 3)
-            if y > 0:
-                up = _get_pixel(basex - stride)
-
-            if filter_type == 1:  # Sub
+            if filter_type == 1:   # Sub
                 color = (color + left) & 0xff
-            elif filter_type == 2:  # Up
+            elif filter_type == 2: # Up
                 color = (color + up) & 0xff
-            elif filter_type == 3:  # Average
+            elif filter_type == 3: # Average
                 color = (color + ((left + up) >> 1)) & 0xff
-            elif filter_type == 4:  # Paeth
-                a = left
-                b = up
-                c = 0
-
-                if x > 2 and y > 0:
-                    c = _get_pixel(basex - stride - 3)
-
+            elif filter_type == 4: # Paeth
+                a, b, c = left, up, _get_pixel(x - 3, y - 1)
                 p = a + b - c
-
-                pa = abs(p - a)
-                pb = abs(p - b)
-                pc = abs(p - c)
-
-                if pa <= pb and pa <= pc:
-                    color = (color + a) & 0xff
-                elif pb <= pc:
-                    color = (color + b) & 0xff
-                else:
-                    color = (color + c) & 0xff
-
-            current_row.append(color)
+                pa, pb, pc = abs(p - a), abs(p - b), abs(p - c)
+                color = (color + (a if pa <= pb and pa <= pc else b if pb <= pc else c)) & 0xff
+            
+            pixels[y].append(color)
 
     return width, height, pixels
 
-
 def write_xattr(path, key, value):
     # This mess below finds the best xattr tool for the job
     try:
@@ -6561,3 +6498,138 @@ def join_nonempty(*values, **kwargs):
     if from_dict is not None:
         values = (traverse_obj(from_dict, variadic(v)) for v in values)
     return delim.join(map(compat_str, filter(None, values)))
+
+
+class Namespace(object):
+    """Immutable namespace"""
+
+    def __init__(self, **kw_attr):
+        self.__dict__.update(kw_attr)
+
+    def __iter__(self):
+        return iter(self.__dict__.values())
+
+    @property
+    def items_(self):
+        return self.__dict__.items()
+
+
+MEDIA_EXTENSIONS = Namespace(
+    common_video=('avi', 'flv', 'mkv', 'mov', 'mp4', 'webm'),
+    video=('3g2', '3gp', 'f4v', 'mk3d', 'divx', 'mpg', 'ogv', 'm4v', 'wmv'),
+    common_audio=('aiff', 'alac', 'flac', 'm4a', 'mka', 'mp3', 'ogg', 'opus', 'wav'),
+    audio=('aac', 'ape', 'asf', 'f4a', 'f4b', 'm4b', 'm4p', 'm4r', 'oga', 'ogx', 'spx', 'vorbis', 'wma', 'weba'),
+    thumbnails=('jpg', 'png', 'webp'),
+    # storyboards=('mhtml', ),
+    subtitles=('srt', 'vtt', 'ass', 'lrc', 'ttml'),
+    manifests=('f4f', 'f4m', 'm3u8', 'smil', 'mpd'),
+)
+MEDIA_EXTENSIONS.video = MEDIA_EXTENSIONS.common_video + MEDIA_EXTENSIONS.video
+MEDIA_EXTENSIONS.audio = MEDIA_EXTENSIONS.common_audio + MEDIA_EXTENSIONS.audio
+
+KNOWN_EXTENSIONS = (
+    MEDIA_EXTENSIONS.video + MEDIA_EXTENSIONS.audio
+    + MEDIA_EXTENSIONS.manifests
+)
+
+
+class _UnsafeExtensionError(Exception):
+    """
+    Mitigation exception for unwanted file overwrite/path traversal
+
+    Ref: https://github.com/yt-dlp/yt-dlp/security/advisories/GHSA-79w7-vh3h-8g4j
+    """
+    _ALLOWED_EXTENSIONS = frozenset(itertools.chain(
+        (   # internal
+            'description',
+            'json',
+            'meta',
+            'orig',
+            'part',
+            'temp',
+            'uncut',
+            'unknown_video',
+            'ytdl',
+        ),
+        # video
+        MEDIA_EXTENSIONS.video, (
+            'avif',
+            'ismv',
+            'm2ts',
+            'm4s',
+            'mng',
+            'mpeg',
+            'qt',
+            'swf',
+            'ts',
+            'vp9',
+            'wvm',
+        ),
+        # audio
+        MEDIA_EXTENSIONS.audio, (
+            'isma',
+            'mid',
+            'mpga',
+            'ra',
+        ),
+        # image
+        MEDIA_EXTENSIONS.thumbnails, (
+            'bmp',
+            'gif',
+            'ico',
+            'heic',
+            'jng',
+            'jpeg',
+            'jxl',
+            'svg',
+            'tif',
+            'wbmp',
+        ),
+        # subtitle
+        MEDIA_EXTENSIONS.subtitles, (
+            'dfxp',
+            'fs',
+            'ismt',
+            'sami',
+            'scc',
+            'ssa',
+            'tt',
+        ),
+        # others
+        MEDIA_EXTENSIONS.manifests,
+        (
+            # not used in yt-dl
+            # *MEDIA_EXTENSIONS.storyboards,
+            # 'desktop',
+            # 'ism',
+            # 'm3u',
+            # 'sbv',
+            # 'swp',
+            # 'url',
+            # 'webloc',
+            # 'xml',
+        )))
+
+    def __init__(self, extension):
+        super(_UnsafeExtensionError, self).__init__('unsafe file extension: {0!r}'.format(extension))
+        self.extension = extension
+
+    # support --no-check-extensions
+    lenient = False
+
+    @classmethod
+    def sanitize_extension(cls, extension, **kwargs):
+        # ... /, *, prepend=False
+        prepend = kwargs.get('prepend', False)
+
+        if '/' in extension or '\\' in extension:
+            raise cls(extension)
+
+        if not prepend:
+            last = extension.rpartition('.')[-1]
+            if last == 'bin':
+                extension = last = 'unknown_video'
+            if not (cls.lenient or last.lower() in cls._ALLOWED_EXTENSIONS):
+                raise cls(extension)
+
+        return extension