From e47691215f75fe7e9684080d17fadf340c9a8450 Mon Sep 17 00:00:00 2001
From: bashonly <88596187+bashonly@users.noreply.github.com>
Date: Wed, 10 Jun 2026 18:00:05 -0500
Subject: [PATCH] Fix `allow-unsafe-ext` compat option (#16920)

Fix bug in e578e265f7c6ca94a74b30e0d8d6196a4d19fb6a

Closes #16919
Authored by: bashonly
---
 test/test_utils.py     | 12 ++++++++++++
 yt_dlp/__init__.py     |  2 +-
 yt_dlp/utils/_utils.py |  5 +++++
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/test/test_utils.py b/test/test_utils.py
index 180ede6240..cd0fb0f2e9 100644
--- a/test/test_utils.py
+++ b/test/test_utils.py
@@ -327,6 +327,12 @@ class TestUtil(unittest.TestCase):
             with self.assertRaises(_UnsafeExtensionError):
                 prepend_extension('abc.unexpected_ext', ext, 'ext')
 
+        # Test allow-unsafe-ext compat option
+        _UnsafeExtensionError._enabled = False
+        self.assertEqual(prepend_extension('abc.ext', 'un/safe'), 'abc.un/safe.ext')
+        # Re-enable sanitization for other tests
+        _UnsafeExtensionError._enabled = True
+
     def test_replace_extension(self):
         self.assertEqual(replace_extension('abc.ext', 'temp'), 'abc.temp')
         self.assertEqual(replace_extension('abc.ext', 'temp', 'ext'), 'abc.temp')
@@ -345,6 +351,12 @@ class TestUtil(unittest.TestCase):
             with self.assertRaises(_UnsafeExtensionError):
                 replace_extension('abc.unexpected_ext', ext, 'ext')
 
+        # Test allow-unsafe-ext compat option
+        _UnsafeExtensionError._enabled = False
+        self.assertEqual(replace_extension('abc.ext', 'bin'), 'abc.bin')
+        # Re-enable sanitization for other tests
+        _UnsafeExtensionError._enabled = True
+
     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')
diff --git a/yt_dlp/__init__.py b/yt_dlp/__init__.py
index 18cf4c8d2c..ec3d52755d 100644
--- a/yt_dlp/__init__.py
+++ b/yt_dlp/__init__.py
@@ -619,7 +619,7 @@ def validate_options(opts):
         warnings.append(
             'Using allow-unsafe-ext opens you up to potential attacks. '
             'Use with great care!')
-        _UnsafeExtensionError.sanitize_extension = lambda x, prepend=False: x
+        _UnsafeExtensionError._enabled = False
 
     return warnings, deprecation_warnings
 
diff --git a/yt_dlp/utils/_utils.py b/yt_dlp/utils/_utils.py
index 56847961ef..43ee53729e 100644
--- a/yt_dlp/utils/_utils.py
+++ b/yt_dlp/utils/_utils.py
@@ -5218,12 +5218,17 @@ class _UnsafeExtensionError(Exception):
         'sbv',
     ])
 
+    _enabled = True
+
     def __init__(self, extension, /):
         super().__init__(f'unsafe file extension: {extension!r}')
         self.extension = extension
 
     @classmethod
     def sanitize_extension(cls, extension, /, *, prepend=False, _allowed_exts=()):
+        if not cls._enabled:
+            return extension
+
         if extension is None:
             return None