GHSA-226f-f24g-524w Open WebUI: Redirect-Bypass SSRF in OAuth `_process_picture_url` (incomplete-fix sibling of CVE-2026-45401)

• PyPI open-webui: < 0.9.6 → fixed in 0.9.6

Summary `backend/open_webui/utils/oauth.py::_process_picture_url` (v0.9.5, lines 1435-1470) calls `validate_url(picture_url)` on the initial URL only, then invokes `aiohttp.ClientSession.get(picture_url, ...)` without `allow_redirects=False`. aiohttp's default is `allow_redirects=True, max_redirects=10`; the function does not pass the project's `AIOHTTP_CLIENT_ALLOW_REDIRECTS` env constant either. An attacker with a valid OAuth IdP identity can therefore submit a public URL that 302-redirects to an internal address and read the internal response body via the attacker's own `profile_image_url` field. This is the same redirect-bypass class as CVE-2026-45401 (GHSA-rh5x-h6pp-cjj6), on a 6th call site that the v0.9.5 patch missed. CVE-2026-45401's advisory body enumerates exactly five affected paths — `SafeWebBaseLoader._scrape`, `_fetch`, `get_content_from_url`, `load_url_image`, `get_image_base64_from_url` — none in `utils/oauth.py`. Vulnerable code (v0.9.5) `backend/open_webui/utils/oauth.py`, lines 1435-1470: ```python async def _process_picture_url(self, picture_url: str, access_token: str = None) -> str: if not picture_url: return '/user.png' try: validate_url(picture_url) # initial URL only get_kwargs = {} if access_token: get_kwargs['headers'] = {'Authorization': f'Bearer {access_token}'} async with aiohttp.ClientSession(trust_env=True) as session: async with session.get(picture_url, get_kwargs, ssl=AIOHTTP_CLIENT_SESSION_SSL) as resp: # ^^^^^^^^^^^ no allow_redirects=False if resp.ok: picture = await resp.read() base64_encoded_picture = base64.b64encode(picture).decode('utf-8') guessed_mime_type = mimetypes.guess_type(picture_url)[0] if guessed_mime_type is None: guessed_mime_type = 'image/jpeg' return f'data:{guessed_mime_type};base64,{base64_encoded_picture}' ... ``` The function is invoked at `oauth.py:1556` (new-user OAuth signup) and `oauth.py:1536` (existing-user picture update on login). Neither call site re-validates after redirect-following. `backend/open_webui/retrieval/web/utils.py` (v0.9.5) imports the env constant `AIOHTTP_CLIENT_ALLOW_REDIRECTS` at line 51 and uses it on the five paths patched by CVE-2026-45401. `utils/oauth.py` does not import or reference it. Exploitation Preconditions: • `ENABLE_OAUTH_SIGNUP=true` or `OAUTH_UPDATE_PICTURE_ON_LOGIN=true` (common in production OAuth-IdP deployments) • Attacker has a valid identity on the configured OAuth IdP (Google, Microsoft, GitHub, or any generic OIDC provider) Steps: 1. Attacker hosts a redirect endpoint at `http://attacker.example/r` on a public IP. `validate_url("http://attacker.example/r")` returns True (`is_global=True` for public IPs). 2. Attacker sets their IdP `picture` claim to `http://attacker.example/r`. 3. Attacker signs in to open-webui via OAuth. open-webui invokes `_process_picture_url("http://attacker.example/r", ...)`. 4. `validate_url` accepts the public URL. `session.get("http://attacker.example/r")` is invoked. 5. attacker.example responds `HTTP/1.1 302 Found\r\nLocation: http://127.0.0.1:11434/api/tags`. (Or `http://169.254.169.254/latest/meta-data/iam/security-credentials/`, RFC1918 internal services, etc.) 6. aiohttp follows the redirect server-side. No re-validation. 7. The internal response body is read into `picture`, base64-encoded, and stored as `profile_image_url = "data:image/jpeg;base64,..."` on the attacker's account. 8. Attacker reads back via `GET /api/v1/auths/`. Decode the base64 payload to get the full internal response body. Impact Full-read SSRF, identical read-back primitive to CVE-2026-45338: • Cloud metadata services (AWS IMDSv1 at `169.254.169.254`, GCP `metadata.google.internal`, Azure IMDS) → IAM credentials, managed-identity tokens • Localhost-bound services (Ollama at `:11434`, Redis, Elasticsearch, internal Postgres exporters) • RFC1918 internal infrastructure not exposed to the internet Distinction from prior CVEs | Prior CVE | This finding | Distinguishing fact | |---|---|---| | CVE-2026-45338 (GHSA-24c9) | `_process_picture_url` had no `validate_url()` call at all | Fixed in v0.9.0 by adding the call. Ours is the call being insufficient because it doesn't loop over redirect targets. Different mechanism, different fix. | | CVE-2026-45400 (GHSA-8w7q) | `validate_url()` had urlparse-vs-requests parser disagreement on `\@` chars | Fixed in v0.9.5 by char-blocklist. Ours is post-validation redirect-following — orthogonal mechanism. | | CVE-2026-45401 (GHSA-rh5x) | Five paths in retrieval, routers/images, utils/files, utils/middleware | Parent class. Same CWE-918 redirect-bypass mechanism. `utils/oauth.py::_process_picture_url` is not among the five paths in the parent advisory's "Affected code paths" section. Same class, missed sink. Direct sibling. | Suggested fix ```python async with session.get( picture_url, get_kwargs, ssl=AIOHTTP_CLIENT_SESSION_SSL, allow_redirects=AIOHTTP_CLIENT_ALLOW_REDIRECTS, # add ) as resp: ``` Or, if redirects must remain enabled by default, wrap in a manual-follow loop that re-invokes `validate_url()` on each `Location` header. This mirrors the fix shape applied to the five paths in CVE-2026-45401. Affected versions Vulnerable: `<= 0.9.5` Fix: 0.9.6 References • CVE-2026-45401 / GHSA-rh5x-h6pp-cjj6 (parent cluster, redirect-bypass on 5 paths) • CVE-2026-45338 / GHSA-24c9-2m8q-qhmh (original `_process_picture_url` SSRF, patched v0.9.0) • CVE-2026-45400 / GHSA-8w7q-q5jp-jvgx (`validate_url` parser-disagreement bypass, patched v0.9.5) • open-webui issue #24560 (corroborates that the v0.9.5 redirect-fix was applied piecemeal across call sites) Proof of Concept End-to-end PoC executed against `ghcr.io/open-webui/open-webui:v0.9.5` in Docker compose. Three services: attacker (OIDC IdP + 302-redirect endpoint on `evil.example.com:9001/redirect`), canary (internal target on `internal-target.local:9002/sentinel`), open-webui v0.9.5. Fresh-CSPRNG sentinel generated after OAuth state-establishing call (per Gate 5.5 oracle protocol): `SSRF-POC-5580111b2a0d7d0c8324bfa92a0d9d09`. Result: • `profile_image_url` field after OAuth login: `data:image/jpeg;base64,U1NSRi1QT0MtNTU4MDExMWIyYTBkN2QwYzgzMjRiZmE5MmEwZDlkMDk=` • Base64 decode: `SSRF-POC-5580111b2a0d7d0c8324bfa92a0d9d09` (byte-for-byte sentinel match) • Canary log: `!!! SSRF HIT - sentinel served` Chain confirmed: OAuth login → IdP returns picture claim `evil.example.com:9001/redirect` → `validate_url()` accepts FQDN → `aiohttp.ClientSession.get(...)` follows 302 to `internal-target.local:9002/sentinel` server-side without re-validation → response body base64-encoded into attacker's `profile_image_url` → readable via `GET /api/v1/auths/`. PoC artifacts (compose, attacker server, canary, run/verify scripts, full transcript) available on request. Reporter Matteo Panzeri — GitHub: `matte1782`, contact: `[email protected]`. Requesting CVE credit as Matteo Panzeri.