Whenever saving an image verify that the binary looks like an image

This should help to head off any future nefariousness

content.py

@@ -15,6 +15,7 @@ import email.parser
 import urllib.parse
 from shutil import copyfile
 from dateutil.parser import parse
+from utils import binary_is_image
 from utils import get_content_from_post
 from utils import get_full_domain
 from utils import get_user_paths
@@ -1648,6 +1649,14 @@ def save_media_in_form_post(media_bytes, debug: bool,
         if not _valid_follows_csv(csv_str):
             return None, None
 
+    # if this is an image then check that the binary looks like an image
+    image_extension_types = get_image_extensions()
+    if detected_extension in image_extension_types:
+        if not binary_is_image(filename, media_bytes[start_pos:]):
+            print('WARN: save_media_in_form_post ' +
+                  'image binary not recognized ' + filename)
+            return None, None
+
     try:
         with open(filename, 'wb') as fp_media:
             fp_media.write(media_bytes[start_pos:])
@@ -2184,40 +2193,3 @@ def add_name_emojis_to_tags(base_dir: str, http_prefix: str,
         if updated:
             new_tag['updated'] = updated
         actor_json['tag'].append(new_tag)
-
-
-def binary_is_image(filename: str, media_binary) -> bool:
-    """Returns true if the given file binary data contains an image
-    """
-    if len(media_binary) < 13:
-        return False
-    filename_lower = filename.lower()
-    bin_is_image = False
-    if filename_lower.endswith('.jpeg') or filename_lower.endswith('jpg'):
-        if media_binary[6:10] in (b'JFIF', b'Exif'):
-            bin_is_image = True
-    elif filename_lower.endswith('.ico'):
-        if media_binary.startswith(b'\x00\x00\x01\x00'):
-            bin_is_image = True
-    elif filename_lower.endswith('.png'):
-        if media_binary.startswith(b'\211PNG\r\n\032\n'):
-            bin_is_image = True
-    elif filename_lower.endswith('.webp'):
-        if media_binary.startswith(b'RIFF') and media_binary[8:12] == b'WEBP':
-            bin_is_image = True
-    elif filename_lower.endswith('.gif'):
-        if media_binary[:6] in (b'GIF87a', b'GIF89a'):
-            bin_is_image = True
-    elif filename_lower.endswith('.avif'):
-        if media_binary[4:12] == b'ftypavif':
-            bin_is_image = True
-    elif filename_lower.endswith('.heic'):
-        if media_binary[4:12] == b'ftypmif1':
-            bin_is_image = True
-    elif filename_lower.endswith('.jxl'):
-        if media_binary.startswith(b'\xff\n'):
-            bin_is_image = True
-    elif filename_lower.endswith('.svg'):
-        if '<svg' in str(media_binary):
-            bin_is_image = True
-    return bin_is_image

daemon.py

@@ -378,10 +378,10 @@ from utils import dangerous_markup
 from utils import refresh_newswire
 from utils import is_image_file
 from utils import has_group_type
+from utils import binary_is_image
 from manualapprove import manual_deny_follow_request_thread
 from manualapprove import manual_approve_follow_request_thread
 from announce import create_announce
-from content import binary_is_image
 from content import add_name_emojis_to_tags
 from content import load_dogwhistles
 from content import valid_url_lengths
@@ -5217,6 +5217,9 @@ class PubServer(BaseHTTPRequestHandler):
         media_filename = \
             media_filename_base + '.' + \
             get_image_extension_from_mime_type(self.headers['Content-type'])
+        if not binary_is_image(media_filename, media_bytes):
+            print('WARN: _receive_image image binary is not recognized ' +
+                  media_filename)
         try:
             with open(media_filename, 'wb') as av_file:
                 av_file.write(media_bytes)

session.py

@@ -13,6 +13,7 @@ from utils import text_in_file
 from utils import acct_dir
 from utils import url_permitted
 from utils import is_image_file
+from utils import binary_is_image
 from httpsig import create_signed_header
 import json
 from socket import error as SocketError
@@ -791,11 +792,16 @@ def download_image(session, url: str, image_filename: str, debug: bool,
                         print('EX: download_image unable to delete ' +
                               image_filename)
             else:
-                with open(image_filename, 'wb') as im_file:
+                media_binary = result.content
-                    im_file.write(result.content)
+                if binary_is_image(image_filename, media_binary):
-                    if debug:
+                    with open(image_filename, 'wb') as im_file:
-                        print('Image downloaded from ' + url)
+                        im_file.write(media_binary)
-                    return True
+                        if debug:
+                            print('Image downloaded from ' + url)
+                        return True
+                else:
+                    print('WARN: download_image binary not recognized ' +
+                          image_filename)
         except BaseException as ex:
             print('EX: Failed to download image: ' +
                   str(url) + ' ' + str(ex))

utils.py

@@ -4540,3 +4540,40 @@ def language_right_to_left(language: str) -> bool:
     if language in rtl_languages:
         return True
     return False
+
+
+def binary_is_image(filename: str, media_binary) -> bool:
+    """Returns true if the given file binary data contains an image
+    """
+    if len(media_binary) < 13:
+        return False
+    filename_lower = filename.lower()
+    bin_is_image = False
+    if filename_lower.endswith('.jpeg') or filename_lower.endswith('jpg'):
+        if media_binary[6:10] in (b'JFIF', b'Exif'):
+            bin_is_image = True
+    elif filename_lower.endswith('.ico'):
+        if media_binary.startswith(b'\x00\x00\x01\x00'):
+            bin_is_image = True
+    elif filename_lower.endswith('.png'):
+        if media_binary.startswith(b'\211PNG\r\n\032\n'):
+            bin_is_image = True
+    elif filename_lower.endswith('.webp'):
+        if media_binary.startswith(b'RIFF') and media_binary[8:12] == b'WEBP':
+            bin_is_image = True
+    elif filename_lower.endswith('.gif'):
+        if media_binary[:6] in (b'GIF87a', b'GIF89a'):
+            bin_is_image = True
+    elif filename_lower.endswith('.avif'):
+        if media_binary[4:12] == b'ftypavif':
+            bin_is_image = True
+    elif filename_lower.endswith('.heic'):
+        if media_binary[4:12] == b'ftypmif1':
+            bin_is_image = True
+    elif filename_lower.endswith('.jxl'):
+        if media_binary.startswith(b'\xff\n'):
+            bin_is_image = True
+    elif filename_lower.endswith('.svg'):
+        if '<svg' in str(media_binary):
+            bin_is_image = True
+    return bin_is_image

webapp_utils.py

@@ -33,10 +33,10 @@ from utils import get_image_extensions
 from utils import local_actor_url
 from utils import text_in_file
 from utils import remove_eol
+from utils import binary_is_image
 from filters import is_filtered
 from cache import get_actor_public_key_from_id
 from cache import store_person_in_cache
-from content import binary_is_image
 from content import add_html_tags
 from content import replace_emoji_from_tags
 from person import get_person_avatar_url
@@ -409,7 +409,8 @@ def update_avatar_image_cache(signing_priv_key_pem: str,
                         return avatar_image_filename.replace(base_dir +
                                                              '/cache', '')
                 else:
-                    print('WARN: avatar image binary not recognized ' +
+                    print('WARN: update_avatar_image_cache ' +
+                          'avatar image binary not recognized ' +
                           actor + ' ' + str(media_binary[0:20]))
         except Exception as ex:
             print('EX: Failed to download avatar image: ' +