Open WebUI: Redirect-Bypass SSRF in OAuth `_process_picture_url` (incomplete-fix sibling of CVE-2026-45401)

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:

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

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.