VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2026-44681: Safety · Authlib OIDC Implicit/Hybrid Authorization Vulnerable to Open Redirect

Affects safetySource GCVE Database

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Not known to be exploited · CVSS 6.1 Medium : upgrade to 3.7.0_11 when convenient.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 3.1 base score

6.1Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 3.7.0_11

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade safety to 3.7.0_11.

Affected software

Product	Affected	Fixed in
Homebrewsafety`pkg:brew/safety`Other threats	Affected >=3.2.4 <3.7.0_11	Fixed in 3.7.0_11

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### 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`: ```python 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: ```python 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`](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. #### Preconditions 1. The server registers `OpenIDImplicitGrant` or `OpenIDHybridGrant` (standard OIDC Implicit or Hybrid flow support). 2. 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`. 3. `scope` does not contain `openid`. 4. 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.

References

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