Malicious Long Unicode filenames may cause a Multiple Application-level Denial of Service

Important: Exploiting this vulnerability requires the attacker to have access to your Frigate instance, which means they could also just delete all of your recordings or perform any other action. If you have configured authentication in front of Frigate via a reverse proxy, then this vulnerability is not exploitable without first getting around your authentication method. For many obvious reasons in addition to this one, please don’t expose your Frigate instance publicly without any kind of authentication.

Summary

When uploading a file or retrieving the filename, a user may intentionally use a large Unicode filename which would lead to a application-level denial of service. This is due to no limitation set on the length of the filename and the costy use of the Unicode normalization with the form NFKD under the hood of secure_filename().

I idenfied multiple vulnerable paths on blakeblackshear/frigate repository. In all of those paths, it was possible for a malicious user to send a filename equals to the output of : python3 -c "print('℀' * 1_000_000)" which would reach the werkzeug secure_filename() call , which in turn under the hood uses a compatibility Unicode normalization with NFKC/NFKD form. In sum, the latter call would be costly in matter of CPU resource and may lead to the application-level denial of service.

Vulnerable Paths

<details>
<summary>Path with 2 steps</summary>

1. frigate/api/media.py
   <pre><code>@MediaBp.route(“/<camera_name>/start/<int:start_ts>/end/<int:end_ts>/clip.mp4”)
   @MediaBp.route(“/<camera_name>/start/<float:start_ts>/end/<float:end_ts>/clip.mp4”)
   def recording_clip(<strong>camera_name</strong>, start_ts, end_ts):
   download = request.args.get(“download”, type=bool)

   </code></pre>

2. frigate/api/media.py
   <pre><code> playlist_lines.append(f"outpoint {int(end_ts - clip.start_time)}")

   file_name = secure_filename(<strong>f"clip_{camera_name}_{start_ts}-{end_ts}.mp4"</strong>)
   path = os.path.join(CACHE_DIR, file_name)
   

   </code></pre>

</details>

---

frigate/api/media.py

<pre><code> playlist_lines.append(f"outpoint {int(end_ts - clip.start_time)}")

file_name = secure_filename(<strong>f"clip_{camera_name}_{start_ts}-{end_ts}.mp4"</strong>)
path = os.path.join(CACHE_DIR, file_name)

</code></pre>

This user-provided value can reach a costly Unicode normalization operation.

Paths

<details>
<summary>Path with 2 steps</summary>

1. frigate/api/media.py
   <pre><code>@MediaBp.route(“/<camera_name>/start/<int:start_ts>/end/<int:end_ts>/clip.mp4”)
   @MediaBp.route(“/<camera_name>/start/<float:start_ts>/end/<float:end_ts>/clip.mp4”)
   def recording_clip(camera_name, <strong>start_ts</strong>, end_ts):
   download = request.args.get(“download”, type=bool)

   </code></pre>

2. frigate/api/media.py
   <pre><code> playlist_lines.append(f"outpoint {int(end_ts - clip.start_time)}")

   file_name = secure_filename(<strong>f"clip_{camera_name}_{start_ts}-{end_ts}.mp4"</strong>)
   path = os.path.join(CACHE_DIR, file_name)
   

   </code></pre>

</details>

---

frigate/api/media.py

<pre><code> playlist_lines.append(f"outpoint {int(end_ts - clip.start_time)}")

file_name = secure_filename(<strong>f"clip_{camera_name}_{start_ts}-{end_ts}.mp4"</strong>)
path = os.path.join(CACHE_DIR, file_name)

</code></pre>

This user-provided value can reach a costly Unicode normalization operation.

Paths

<details>
<summary>Path with 2 steps</summary>

1. frigate/api/media.py
   <pre><code>@MediaBp.route(“/<camera_name>/start/<int:start_ts>/end/<int:end_ts>/clip.mp4”)
   @MediaBp.route(“/<camera_name>/start/<float:start_ts>/end/<float:end_ts>/clip.mp4”)
   def recording_clip(camera_name, start_ts, <strong>end_ts</strong>):
   download = request.args.get(“download”, type=bool)

   </code></pre>

2. frigate/api/media.py
   <pre><code> playlist_lines.append(f"outpoint {int(end_ts - clip.start_time)}")

   file_name = secure_filename(<strong>f"clip_{camera_name}_{start_ts}-{end_ts}.mp4"</strong>)
   path = os.path.join(CACHE_DIR, file_name)
   

   </code></pre>

</details>

---

frigate/api/media.py

<pre><code> current_app.frigate_config,
camera_name,
secure_filename(<strong>name.replace(" ", “_”)</strong>) if name else None,
int(start_time),
int(end_time),
</code></pre>

This user-provided value can reach a costly Unicode normalization operation.

Paths

<details>
<summary>Path with 8 steps</summary>

1. frigate/api/media.py
   <pre><code> jsonify,
   make_response,
   <strong>request</strong>,
   )
   from peewee import DoesNotExist, fn
   </code></pre>

2. frigate/api/media.py
   <pre><code> jsonify,
   make_response,
   <strong>request</strong>,
   )
   from peewee import DoesNotExist, fn
   </code></pre>

3. frigate/api/media.py
   <pre><code> )

   json: dict[str, any] = <strong>request</strong>.get_json(silent=True) or {}
   playback_factor = json.get("playback", "realtime")
   name: Optional[str] = json.get("name")
   

   </code></pre>

4. frigate/api/media.py
   <pre><code> )

   <strong>json</strong>: dict[str, any] = request.get_json(silent=True) or {}
   playback_factor = json.get("playback", "realtime")
   name: Optional[str] = json.get("name")
   

   </code></pre>

5. frigate/api/media.py
   <pre><code> json: dict[str, any] = request.get_json(silent=True) or {}
   playback_factor = json.get(“playback”, “realtime”)
   name: Optional[str] = <strong>json</strong>.get(“name”)

   recordings_count = (
   

   </code></pre>

6. frigate/api/media.py
   <pre><code> json: dict[str, any] = request.get_json(silent=True) or {}
   playback_factor = json.get(“playback”, “realtime”)
   name: Optional[str] = <strong>json.get(“name”)</strong>

   recordings_count = (
   

   </code></pre>

7. frigate/api/media.py
   <pre><code> json: dict[str, any] = request.get_json(silent=True) or {}
   playback_factor = json.get(“playback”, “realtime”)
   <strong>name</strong>: Optional[str] = json.get(“name”)

   recordings_count = (
   

   </code></pre>

8. frigate/api/media.py
   <pre><code> current_app.frigate_config,
   camera_name,
   secure_filename(<strong>name.replace(" ", “_”)</strong>) if name else None,
   int(start_time),
   int(end_time),
   </code></pre>

</details>

---

frigate/api/media.py

<pre><code>def export_rename(file_name_current, file_name_new: str):
safe_file_name_current = secure_filename(
<strong>export_filename_check_extension(file_name_current)</strong>
)
file_current = os.path.join(EXPORT_DIR, safe_file_name_current)
</code></pre>

This user-provided value can reach a costly Unicode normalization operation.

Paths

<details>
<summary>Path with 5 steps</summary>

1. frigate/api/media.py
   <pre><code>
   @MediaBp.route(“/export/<file_name_current>/<file_name_new>”, methods=[“PATCH”])
   def export_rename(<strong>file_name_current</strong>, file_name_new: str):
   safe_file_name_current = secure_filename(
   export_filename_check_extension(file_name_current)
   </code></pre>

2. frigate/api/media.py
   <pre><code>def export_rename(file_name_current, file_name_new: str):
   safe_file_name_current = secure_filename(
   export_filename_check_extension(<strong>file_name_current</strong>)
   )
   file_current = os.path.join(EXPORT_DIR, safe_file_name_current)
   </code></pre>

3. frigate/api/media.py
   <pre><code>

   def export_filename_check_extension(<strong>filename</strong>: str):
   if filename.endswith(“.mp4”):
   return filename
   </code></pre>

4. frigate/api/media.py
   <pre><code>def export_filename_check_extension(filename: str):
   if filename.endswith(“.mp4”):
   return <strong>filename</strong>
   else:
   return filename + “.mp4”
   </code></pre>

5. frigate/api/media.py
   <pre><code>def export_rename(file_name_current, file_name_new: str):
   safe_file_name_current = secure_filename(
   <strong>export_filename_check_extension(file_name_current)</strong>
   )
   file_current = os.path.join(EXPORT_DIR, safe_file_name_current)
   </code></pre>

</details>

<details>
<summary>Path with 5 steps</summary>

1. frigate/api/media.py
   <pre><code>
   @MediaBp.route(“/export/<file_name_current>/<file_name_new>”, methods=[“PATCH”])
   def export_rename(<strong>file_name_current</strong>, file_name_new: str):
   safe_file_name_current = secure_filename(
   export_filename_check_extension(file_name_current)
   </code></pre>

2. frigate/api/media.py
   <pre><code>def export_rename(file_name_current, file_name_new: str):
   safe_file_name_current = secure_filename(
   export_filename_check_extension(<strong>file_name_current</strong>)
   )
   file_current = os.path.join(EXPORT_DIR, safe_file_name_current)
   </code></pre>

3. frigate/api/media.py
   <pre><code>

   def export_filename_check_extension(<strong>filename</strong>: str):
   if filename.endswith(“.mp4”):
   return filename
   </code></pre>

4. frigate/api/media.py
   <pre><code> return filename
   else:
   return <strong>filename + “.mp4”</strong>

   </code></pre>

5. frigate/api/media.py
   <pre><code>def export_rename(file_name_current, file_name_new: str):
   safe_file_name_current = secure_filename(
   <strong>export_filename_check_extension(file_name_current)</strong>
   )
   file_current = os.path.join(EXPORT_DIR, safe_file_name_current)
   </code></pre>

</details>

---

frigate/api/media.py

<pre><code> )

safe_file_name_new = secure_filename(<strong>export_filename_check_extension(file_name_new)</strong>)
file_new = os.path.join(EXPORT_DIR, safe_file_name_new)

</code></pre>

This user-provided value can reach a costly Unicode normalization operation.

Paths

<details>
<summary>Path with 5 steps</summary>

1. frigate/api/media.py
   <pre><code>
   @MediaBp.route(“/export/<file_name_current>/<file_name_new>”, methods=[“PATCH”])
   def export_rename(file_name_current, <strong>file_name_new</strong>: str):
   safe_file_name_current = secure_filename(
   export_filename_check_extension(file_name_current)
   </code></pre>

2. frigate/api/media.py
   <pre><code> )

   safe_file_name_new = secure_filename(export_filename_check_extension(<strong>file_name_new</strong>))
   file_new = os.path.join(EXPORT_DIR, safe_file_name_new)
   

   </code></pre>

3. frigate/api/media.py
   <pre><code>

   def export_filename_check_extension(<strong>filename</strong>: str):
   if filename.endswith(“.mp4”):
   return filename
   </code></pre>

4. frigate/api/media.py
   <pre><code>def export_filename_check_extension(filename: str):
   if filename.endswith(“.mp4”):
   return <strong>filename</strong>
   else:
   return filename + “.mp4”
   </code></pre>

5. frigate/api/media.py
   <pre><code> )

   safe_file_name_new = secure_filename(<strong>export_filename_check_extension(file_name_new)</strong>)
   file_new = os.path.join(EXPORT_DIR, safe_file_name_new)
   

   </code></pre>

</details>

<details>
<summary>Path with 5 steps</summary>

1. frigate/api/media.py
   <pre><code>
   @MediaBp.route(“/export/<file_name_current>/<file_name_new>”, methods=[“PATCH”])
   def export_rename(file_name_current, <strong>file_name_new</strong>: str):
   safe_file_name_current = secure_filename(
   export_filename_check_extension(file_name_current)
   </code></pre>

2. frigate/api/media.py
   <pre><code> )

   safe_file_name_new = secure_filename(export_filename_check_extension(<strong>file_name_new</strong>))
   file_new = os.path.join(EXPORT_DIR, safe_file_name_new)
   

   </code></pre>

3. frigate/api/media.py
   <pre><code>

   def export_filename_check_extension(<strong>filename</strong>: str):
   if filename.endswith(“.mp4”):
   return filename
   </code></pre>

4. frigate/api/media.py
   <pre><code> return filename
   else:
   return <strong>filename + “.mp4”</strong>

   </code></pre>

5. frigate/api/media.py
   <pre><code> )

   safe_file_name_new = secure_filename(<strong>export_filename_check_extension(file_name_new)</strong>)
   file_new = os.path.join(EXPORT_DIR, safe_file_name_new)
   

   </code></pre>

</details>

---

frigate/api/media.py

<pre><code>@MediaBp.route(“/export/<file_name>”, methods=[“DELETE”])
def export_delete(file_name: str):
safe_file_name = secure_filename(<strong>export_filename_check_extension(file_name)</strong>)
file = os.path.join(EXPORT_DIR, safe_file_name)

</code></pre>

This user-provided value can reach a costly Unicode normalization operation.

Paths

<details>
<summary>Path with 5 steps</summary>

1. frigate/api/media.py
   <pre><code>
   @MediaBp.route(“/export/<file_name>”, methods=[“DELETE”])
   def export_delete(<strong>file_name</strong>: str):
   safe_file_name = secure_filename(export_filename_check_extension(file_name))
   file = os.path.join(EXPORT_DIR, safe_file_name)
   </code></pre>

2. frigate/api/media.py
   <pre><code>@MediaBp.route(“/export/<file_name>”, methods=[“DELETE”])
   def export_delete(file_name: str):
   safe_file_name = secure_filename(export_filename_check_extension(<strong>file_name</strong>))
   file = os.path.join(EXPORT_DIR, safe_file_name)

   </code></pre>

3. frigate/api/media.py
   <pre><code>

   def export_filename_check_extension(<strong>filename</strong>: str):
   if filename.endswith(“.mp4”):
   return filename
   </code></pre>

4. frigate/api/media.py
   <pre><code>def export_filename_check_extension(filename: str):
   if filename.endswith(“.mp4”):
   return <strong>filename</strong>
   else:
   return filename + “.mp4”
   </code></pre>

5. frigate/api/media.py
   <pre><code>@MediaBp.route(“/export/<file_name>”, methods=[“DELETE”])
   def export_delete(file_name: str):
   safe_file_name = secure_filename(<strong>export_filename_check_extension(file_name)</strong>)
   file = os.path.join(EXPORT_DIR, safe_file_name)

   </code></pre>

</details>

<details>
<summary>Path with 5 steps</summary>

1. frigate/api/media.py
   <pre><code>
   @MediaBp.route(“/export/<file_name>”, methods=[“DELETE”])
   def export_delete(<strong>file_name</strong>: str):
   safe_file_name = secure_filename(export_filename_check_extension(file_name))
   file = os.path.join(EXPORT_DIR, safe_file_name)
   </code></pre>

2. frigate/api/media.py
   <pre><code>@MediaBp.route(“/export/<file_name>”, methods=[“DELETE”])
   def export_delete(file_name: str):
   safe_file_name = secure_filename(export_filename_check_extension(<strong>file_name</strong>))
   file = os.path.join(EXPORT_DIR, safe_file_name)

   </code></pre>

3. frigate/api/media.py
   <pre><code>

   def export_filename_check_extension(<strong>filename</strong>: str):
   if filename.endswith(“.mp4”):
   return filename
   </code></pre>

4. frigate/api/media.py
   <pre><code> return filename
   else:
   return <strong>filename + “.mp4”</strong>

   </code></pre>

5. frigate/api/media.py
   <pre><code>@MediaBp.route(“/export/<file_name>”, methods=[“DELETE”])
   def export_delete(file_name: str):
   safe_file_name = secure_filename(<strong>export_filename_check_extension(file_name)</strong>)
   file = os.path.join(EXPORT_DIR, safe_file_name)

   </code></pre>

</details>

---

frigate/api/media.py

<pre><code>def preview_thumbnail(file_name: str):
“”“Get a thumbnail from the cached preview frames.”“”
safe_file_name_current = secure_filename(<strong>file_name</strong>)
preview_dir = os.path.join(CACHE_DIR, “preview_frames”)

</code></pre>

This user-provided value can reach a costly Unicode normalization operation.

Paths

<details>
<summary>Path with 2 steps</summary>

1. frigate/api/media.py
   <pre><code>@MediaBp.route(“/preview/<file_name>/thumbnail.jpg”)
   @MediaBp.route(“/preview/<file_name>/thumbnail.webp”)
   def preview_thumbnail(<strong>file_name</strong>: str):
   “”“Get a thumbnail from the cached preview frames.”“”
   safe_file_name_current = secure_filename(file_name)
   </code></pre>

2. frigate/api/media.py
   <pre><code>def preview_thumbnail(file_name: str):
   “”“Get a thumbnail from the cached preview frames.”“”
   safe_file_name_current = secure_filename(<strong>file_name</strong>)
   preview_dir = os.path.join(CACHE_DIR, “preview_frames”)

   </code></pre>

</details>

Impact

• Application-level Denial of Service, the web app would hung undefinetly and not process any further request due to the use of the malicious payload.

Mitigation

• Limiting the length of the incoming filename, similar to this commit fix.

References

• Similar to CVE-2023-46695