Vulnerability-Lookup

GHSA-R95X-QFJJ-FJJ2

Vulnerability from github – Published: 2026-05-13 01:36 – Updated: 2026-05-13 01:36

Summary

Authlib OIDC Implicit/Hybrid Authorization Vulnerable to Open Redirect

Details

Summary

An unauthenticated open redirect in Authlib's OpenIDImplicitGrant and OpenIDHybridGrant authorization endpoint lets a remote attacker cause the authorization server to issue an HTTP 302 to an attacker-chosen URL by submitting an authorization request that omits the openid scope.

Details

Vulnerable code

OpenIDImplicitGrant.validate_authorization_request in authlib/oidc/core/grants/implicit.py:

def validate_authorization_request(self):
    if not is_openid_scope(self.request.payload.scope):
        raise InvalidScopeError(
            "Missing 'openid' scope",
            redirect_uri=self.request.payload.redirect_uri,  # ← raw, unvalidated
            redirect_fragment=True,
        )
    redirect_uri = super().validate_authorization_request()
    ...

OpenIDHybridGrant.validate_authorization_request in authlib/oidc/core/grants/hybrid.py shares the same pattern.

Root cause

Both methods perform the openid scope presence check before delegating to super().validate_authorization_request(), which is where AuthorizationEndpointMixin.validate_authorization_redirect_uri validates the requested redirect_uri against the client's check_redirect_uri(...). The InvalidScopeError thrown by the scope check therefore carries attacker-controlled self.request.payload.redirect_uri.

OAuth2Error.__call__ in authlib/oauth2/base.py renders any error with a non-empty redirect_uri as an HTTP 302:

def __call__(self, uri=None):
    if self.redirect_uri:
        params = self.get_body()
        loc = add_params_to_uri(self.redirect_uri, params, self.redirect_fragment)
        return 302, "", [("Location", loc)]
    return super().__call__(uri=uri)

A malformed authorization request that selects OpenIDImplicitGrant or OpenIDHybridGrant and omits the openid scope is therefore redirected to a fully attacker-chosen URL.

This is a variant of the issue fixed in commit 3be08468 ("fix: redirecting to unvalidated redirect_uri on UnsupportedResponseTypeError") that was missed in the OIDC Implicit and Hybrid grants.

Preconditions

The server registers OpenIDImplicitGrant or OpenIDHybridGrant (standard OIDC Implicit or Hybrid flow support).
The attacker's request uses a response_type that matches either grant: id_token, id_token token, code id_token, code token, or code id_token token.
scope does not contain openid.
Any redirect_uri value.

No user authentication, no consent, no valid session, no CSRF token, and — notably — no valid client_id are required. The scope check runs before any client lookup, so any client_id value (including nonexistent ones) reaches the vulnerable code path.

PoC

The following unauthenticated GET is sufficient to induce the authorization server to redirect a victim's browser to an attacker-controlled URL:

GET /oauth/authorize
    ?response_type=id_token
    &client_id=anything
    &scope=profile
    &redirect_uri=https%3A%2F%2Fevil.example.com%2Fphish
    &state=s&nonce=n  HTTP/1.1
Host: victim-op.example

Server response:

HTTP/1.1 302 Found
Location: https://evil.example.com/phish#error=invalid_scope&error_description=Missing+%27openid%27+scope&state=s

Impact

Open redirect from a trusted authorization server origin. Victims receiving a phishing link see the legitimate OIDC provider's domain in the URL bar at the moment they click. The authorization server itself issues the 302 to the attacker's page, lending the attacker's landing page the OP's reputation and potentially satisfying domain-allow-list controls that trust the OP.
Phishing / credential harvesting leverage. The attacker's page can mimic the legitimate OP's consent screen or a relying-party error page to solicit credentials, MFA codes, or to continue a downstream confused-deputy attack.
RFC violation. RFC 6749 §4.1.2.1 and RFC 9700 (OAuth 2.0 Security BCP) §4.11 both state that an authorization server MUST NOT perform redirection to a redirect_uri that has not been validated against the client's registered URIs, even in error responses. The state parameter is echoed back, giving the attacker site a stable correlator.
No direct token/code leak. This flaw fires before any authorization decision, so no authorization codes, ID tokens, or access tokens are disclosed. The impact is limited to open-redirect phishing leverage. Combined with other issues (e.g., downstream SSO trust chains) it may contribute to account-takeover chains; on its own it is a Medium-severity open redirect.

Affected deployments

Any application using Authlib as an OIDC provider that registers OpenIDImplicitGrant and/or OpenIDHybridGrant — i.e. anyone supporting the Implicit flow or the Hybrid flow (response_type=code id_token, etc.) — is affected. Clients of an Authlib-based OP are not directly affected; this is a server-side issue.

Authorization servers that only register the plain AuthorizationCodeGrant (code flow, with or without PKCE and the OpenIDCode extension) are not affected by this specific variant: the code-flow grant validates redirect_uri before raising scope errors. If you were affected by the sibling issue fixed in 3be08468 (UnsupportedResponseTypeError), you should already be on 1.6.10 or later; this advisory is independent of that fix.

Suggested fix

The attached fix-oidc-open-redirect.patch reorders each method to delegate to its super (or call validate_code_authorization_request for Hybrid) first, and then performs the openid-scope check with the validated redirect_uri variable.

# authlib/oidc/core/grants/implicit.py
def validate_authorization_request(self):
    redirect_uri = super().validate_authorization_request()   # runs client + redirect_uri validation
    if not is_openid_scope(self.request.payload.scope):
        raise InvalidScopeError(
            "Missing 'openid' scope",
            redirect_uri=redirect_uri,                         # validated
            redirect_fragment=True,
        )
    try:
        validate_nonce(self.request, self.exists_nonce, required=True)
    except OAuth2Error as error:
        error.redirect_uri = redirect_uri
        error.redirect_fragment = True
        raise error
    return redirect_uri

An equivalent transform is applied to OpenIDHybridGrant.validate_authorization_request, invoking validate_code_authorization_request first and only then checking is_openid_scope.

Alternatively, inline a client = query_client(request.payload.client_id) + client.check_redirect_uri(request.payload.redirect_uri) guard before populating redirect_uri on the error — the pattern used in 3be08468.

The patch also adds regression tests analogous to test_unsupported_response_type_does_not_redirect from commit 3be08468, asserting rv.status_code == 400 and rv.headers.get("Location") is None for an unregistered redirect_uri with a non-openid scope.

Workarounds

No clean server-side workaround exists short of patching. Partial mitigations:

Unregister OpenIDImplicitGrant and OpenIDHybridGrant if the Implicit and Hybrid flows are not required. (RFC 9700 deprecates the Implicit flow and discourages Hybrid flows, so this is recommended anyway.)
Front the /authorize endpoint with a reverse proxy rule that rejects requests containing both a redirect_uri parameter and a scope that does not include openid when response_type matches the vulnerable set. This is fragile and not recommended as a primary control.

References

RFC 6749, §4.1.2.1 — Error Response (OAuth 2.0 authorization endpoint)
RFC 9700, §4.11 — Redirect URI validation
OpenID Connect Core 1.0, §3.2.2.6 / §3.3.2.6 — Authentication Error Response
Authlib commit 3be08468 — prior fix for the same class of issue in UnsupportedResponseTypeError (Authlib 1.6.10)
Authlib source (by symbol; verified in commit 5d2e603e):
OpenIDImplicitGrant.validate_authorization_request — authlib/oidc/core/grants/implicit.py
OpenIDHybridGrant.validate_authorization_request — authlib/oidc/core/grants/hybrid.py
OAuth2Error.__call__ — authlib/oauth2/base.py (renders errors with redirect_uri as HTTP 302)
AuthorizationEndpointMixin.validate_authorization_redirect_uri — authlib/oauth2/rfc6749/grants/base.py (the validation that is bypassed)

Severity

6.1 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "authlib"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.7.0"
            },
            {
              "fixed": "1.7.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.7.0"
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.6.11"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "authlib"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.6.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-44681"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-601",
      "CWE-863"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-13T01:36:03Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nAn unauthenticated open redirect in Authlib\u0027s `OpenIDImplicitGrant` and `OpenIDHybridGrant` authorization endpoint lets a remote attacker cause the authorization server to issue an HTTP 302 to an attacker-chosen URL by submitting an authorization request that omits the `openid` scope.\n\n### Details\n\n#### Vulnerable code\n\n`OpenIDImplicitGrant.validate_authorization_request` in `authlib/oidc/core/grants/implicit.py`:\n\n```python\ndef validate_authorization_request(self):\n    if not is_openid_scope(self.request.payload.scope):\n        raise InvalidScopeError(\n            \"Missing \u0027openid\u0027 scope\",\n            redirect_uri=self.request.payload.redirect_uri,  # \u2190 raw, unvalidated\n            redirect_fragment=True,\n        )\n    redirect_uri = super().validate_authorization_request()\n    ...\n```\n\n`OpenIDHybridGrant.validate_authorization_request` in `authlib/oidc/core/grants/hybrid.py` shares the same pattern.\n\n#### Root cause\n\nBoth methods perform the `openid` scope presence check before delegating to `super().validate_authorization_request()`, which is where `AuthorizationEndpointMixin.validate_authorization_redirect_uri` validates the requested `redirect_uri` against the client\u0027s `check_redirect_uri(...)`. The `InvalidScopeError` thrown by the scope check therefore carries attacker-controlled `self.request.payload.redirect_uri`.\n\n`OAuth2Error.__call__` in `authlib/oauth2/base.py` renders any error with a non-empty `redirect_uri` as an HTTP 302:\n\n```python\ndef __call__(self, uri=None):\n    if self.redirect_uri:\n        params = self.get_body()\n        loc = add_params_to_uri(self.redirect_uri, params, self.redirect_fragment)\n        return 302, \"\", [(\"Location\", loc)]\n    return super().__call__(uri=uri)\n```\n\nA malformed authorization request that selects `OpenIDImplicitGrant` or `OpenIDHybridGrant` and omits the `openid` scope is therefore redirected to a fully attacker-chosen URL.\n\nThis is a variant of the issue fixed in commit [`3be08468`](https://github.com/authlib/authlib/commit/3be08468) (\"fix: redirecting to unvalidated `redirect_uri` on `UnsupportedResponseTypeError`\") that was missed in the OIDC Implicit and Hybrid grants.\n\n#### Preconditions\n\n1. The server registers `OpenIDImplicitGrant` or `OpenIDHybridGrant` (standard OIDC Implicit or Hybrid flow support).\n2. The attacker\u0027s request uses a `response_type` that matches either grant: `id_token`, `id_token token`, `code id_token`, `code token`, or `code id_token token`.\n3. `scope` does not contain `openid`.\n4. Any `redirect_uri` value.\n\nNo user authentication, no consent, no valid session, no CSRF token, and \u2014 notably \u2014 no valid `client_id` are required. The scope check runs before any client lookup, so any `client_id` value (including nonexistent ones) reaches the vulnerable code path.\n\n### PoC\n\nThe following unauthenticated GET is sufficient to induce the authorization server to redirect a victim\u0027s browser to an attacker-controlled URL:\n\n```\nGET /oauth/authorize\n    ?response_type=id_token\n    \u0026client_id=anything\n    \u0026scope=profile\n    \u0026redirect_uri=https%3A%2F%2Fevil.example.com%2Fphish\n    \u0026state=s\u0026nonce=n  HTTP/1.1\nHost: victim-op.example\n```\n\nServer response:\n\n```\nHTTP/1.1 302 Found\nLocation: https://evil.example.com/phish#error=invalid_scope\u0026error_description=Missing+%27openid%27+scope\u0026state=s\n```\n\n### Impact\n\n- Open redirect from a trusted authorization server origin. Victims receiving a phishing link see the legitimate OIDC provider\u0027s domain in the URL bar at the moment they click. The authorization server itself issues the 302 to the attacker\u0027s page, lending the attacker\u0027s landing page the OP\u0027s reputation and potentially satisfying domain-allow-list controls that trust the OP.\n- Phishing / credential harvesting leverage. The attacker\u0027s page can mimic the legitimate OP\u0027s consent screen or a relying-party error page to solicit credentials, MFA codes, or to continue a downstream confused-deputy attack.\n- RFC violation. RFC 6749 \u00a74.1.2.1 and RFC 9700 (OAuth 2.0 Security BCP) \u00a74.11 both state that an authorization server MUST NOT perform redirection to a `redirect_uri` that has not been validated against the client\u0027s registered URIs, even in error responses. The `state` parameter is echoed back, giving the attacker site a stable correlator.\n- No direct token/code leak. This flaw fires before any authorization decision, so no authorization codes, ID tokens, or access tokens are disclosed. The impact is limited to open-redirect phishing leverage. Combined with other issues (e.g., downstream SSO trust chains) it may contribute to account-takeover chains; on its own it is a Medium-severity open redirect.\n\n#### Affected deployments\n\nAny application using Authlib as an OIDC provider that registers `OpenIDImplicitGrant` and/or `OpenIDHybridGrant` \u2014 i.e. anyone supporting the Implicit flow or the Hybrid flow (`response_type=code id_token`, etc.) \u2014 is affected. Clients of an Authlib-based OP are not directly affected; this is a server-side issue.\n\nAuthorization servers that only register the plain `AuthorizationCodeGrant` (code flow, with or without PKCE and the `OpenIDCode` extension) are not affected by this specific variant: the code-flow grant validates `redirect_uri` before raising scope errors. If you were affected by the sibling issue fixed in `3be08468` (`UnsupportedResponseTypeError`), you should already be on `1.6.10` or later; this advisory is independent of that fix.\n\n### Suggested fix\n\nThe attached `fix-oidc-open-redirect.patch` reorders each method to delegate to its super (or call `validate_code_authorization_request` for Hybrid) first, and then performs the `openid`-scope check with the validated `redirect_uri` variable.\n\n```python\n# authlib/oidc/core/grants/implicit.py\ndef validate_authorization_request(self):\n    redirect_uri = super().validate_authorization_request()   # runs client + redirect_uri validation\n    if not is_openid_scope(self.request.payload.scope):\n        raise InvalidScopeError(\n            \"Missing \u0027openid\u0027 scope\",\n            redirect_uri=redirect_uri,                         # validated\n            redirect_fragment=True,\n        )\n    try:\n        validate_nonce(self.request, self.exists_nonce, required=True)\n    except OAuth2Error as error:\n        error.redirect_uri = redirect_uri\n        error.redirect_fragment = True\n        raise error\n    return redirect_uri\n```\n\nAn equivalent transform is applied to `OpenIDHybridGrant.validate_authorization_request`, invoking `validate_code_authorization_request` first and only then checking `is_openid_scope`.\n\nAlternatively, inline a `client = query_client(request.payload.client_id)` + `client.check_redirect_uri(request.payload.redirect_uri)` guard before populating `redirect_uri` on the error \u2014 the pattern used in `3be08468`.\n\nThe patch also adds regression tests analogous to `test_unsupported_response_type_does_not_redirect` from commit `3be08468`, asserting `rv.status_code == 400` and `rv.headers.get(\"Location\") is None` for an unregistered `redirect_uri` with a non-`openid` scope.\n\n### Workarounds\n\nNo clean server-side workaround exists short of patching. Partial mitigations:\n\n- Unregister `OpenIDImplicitGrant` and `OpenIDHybridGrant` if the Implicit and Hybrid flows are not required. (RFC 9700 deprecates the Implicit flow and discourages Hybrid flows, so this is recommended anyway.)\n- Front the `/authorize` endpoint with a reverse proxy rule that rejects requests containing both a `redirect_uri` parameter and a `scope` that does not include `openid` when `response_type` matches the vulnerable set. This is fragile and not recommended as a primary control.\n\n### References\n\n- RFC 6749, \u00a74.1.2.1 \u2014 Error Response (OAuth 2.0 authorization endpoint)\n- RFC 9700, \u00a74.11 \u2014 Redirect URI validation\n- OpenID Connect Core 1.0, \u00a73.2.2.6 / \u00a73.3.2.6 \u2014 Authentication Error Response\n- Authlib commit [`3be08468`](https://github.com/authlib/authlib/commit/3be08468) \u2014 prior fix for the same class of issue in `UnsupportedResponseTypeError` (Authlib 1.6.10)\n- Authlib source (by symbol; verified in commit `5d2e603e`):\n  - `OpenIDImplicitGrant.validate_authorization_request` \u2014 `authlib/oidc/core/grants/implicit.py`\n  - `OpenIDHybridGrant.validate_authorization_request` \u2014 `authlib/oidc/core/grants/hybrid.py`\n  - `OAuth2Error.__call__` \u2014 `authlib/oauth2/base.py` (renders errors with `redirect_uri` as HTTP 302)\n  - `AuthorizationEndpointMixin.validate_authorization_redirect_uri` \u2014 `authlib/oauth2/rfc6749/grants/base.py` (the validation that is bypassed)",
  "id": "GHSA-r95x-qfjj-fjj2",
  "modified": "2026-05-13T01:36:03Z",
  "published": "2026-05-13T01:36:03Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/authlib/authlib/security/advisories/GHSA-r95x-qfjj-fjj2"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/authlib/authlib"
    },
    {
      "type": "WEB",
      "url": "https://github.com/authlib/authlib/releases/tag/v1.6.12"
    },
    {
      "type": "WEB",
      "url": "https://github.com/authlib/authlib/releases/tag/v1.7.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Authlib OIDC Implicit/Hybrid Authorization Vulnerable to Open Redirect"
}

CVE-2026-44681 (GCVE-0-2026-44681)

Vulnerability from cvelistv5 – Published: 2026-05-27 19:20 – Updated: 2026-05-27 19:20

Title

Authlib: Open Redirect in Authlib OIDC Implicit/Hybrid Authorization

Summary

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.6.12 and 1.7.1, an unauthenticated open redirect in Authlib's OpenIDImplicitGrant and OpenIDHybridGrant authorization endpoint lets a remote attacker cause the authorization server to issue an HTTP 302 to an attacker-chosen URL by submitting an authorization request that omits the openid scope. This vulnerability is fixed in 1.6.12 and 1.7.1.

Severity

6.1 (Medium)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CWE

CWE-601 - URL Redirection to Untrusted Site ('Open Redirect')
CWE-863 - Incorrect Authorization

Assigner

GitHub_M

References

1 reference

URL	Tags
https://github.com/authlib/authlib/security/advis…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
authlib	authlib	Affected: < 1.6.12 Affected: >= 1.7.0, < 1.7.1

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JSON

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "authlib",
          "vendor": "authlib",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.6.12"
            },
            {
              "status": "affected",
              "version": "\u003e= 1.7.0, \u003c 1.7.1"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.6.12 and 1.7.1, an unauthenticated open redirect in Authlib\u0027s OpenIDImplicitGrant and OpenIDHybridGrant authorization endpoint lets a remote attacker cause the authorization server to issue an HTTP 302 to an attacker-chosen URL by submitting an authorization request that omits the openid scope. This vulnerability is fixed in 1.6.12 and 1.7.1."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 6.1,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "LOW",
            "integrityImpact": "LOW",
            "privilegesRequired": "NONE",
            "scope": "CHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-601",
              "description": "CWE-601: URL Redirection to Untrusted Site (\u0027Open Redirect\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-863",
              "description": "CWE-863: Incorrect Authorization",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-27T19:20:44.122Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/authlib/authlib/security/advisories/GHSA-r95x-qfjj-fjj2",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/authlib/authlib/security/advisories/GHSA-r95x-qfjj-fjj2"
        }
      ],
      "source": {
        "advisory": "GHSA-r95x-qfjj-fjj2",
        "discovery": "UNKNOWN"
      },
      "title": "Authlib: Open Redirect in Authlib OIDC Implicit/Hybrid Authorization"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-44681",
    "datePublished": "2026-05-27T19:20:44.122Z",
    "dateReserved": "2026-05-07T16:20:08.660Z",
    "dateUpdated": "2026-05-27T19:20:44.122Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-R95X-QFJJ-FJJ2

Summary

Details

Vulnerable code

Root cause

Preconditions

PoC

Impact

Affected deployments

Suggested fix

Workarounds

References

CVE-2026-44681 (GCVE-0-2026-44681)

Tags

Sightings

Nomenclature