OAuthLib up to 3.x Token Grant improper authorization

Summaryinfo

A vulnerability was found in OAuthLib up to 3.x. It has been rated as critical. The affected element is an unknown function of the component Token Grant Handler. The manipulation leads to improper authorization. This vulnerability is referenced as CVE-2026-118669. Remote exploitation of the attack is possible. No exploit is available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in OAuthLib up to 3.x and classified as critical. This issue affects an unknown function of the component Token Grant Handler. The manipulation with an unknown input leads to a improper authorization vulnerability. Using CWE to declare the problem leads to CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

OAuthLib is an implementation of the OAuth request-signing logic for Python 3.6+. Prior to 4.0.0, the client_credentials and Resource Owner Password Credentials token grant handlers can authenticate request.client as one confidential client while retaining an attacker-supplied request.client_id for validate_grant_type and validate_scopes. A lower-privilege authenticated client can therefore cause grant and scope authorization to use another client's identity when an application validator relies on the documented client_id argument, potentially issuing tokens with unauthorized grants or scopes. Validators that authorize exclusively from request.client may not be affected. This issue is fixed in version 4.0.0.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-118669 since 10/28/2026. The exploitation is known to be easy. The attack may be initiated remotely. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1548.002 for this issue.

Upgrading to version 4.0.0 eliminates this vulnerability.

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Productinfo

Name

• OAuthLib

Version

• 3.x

Website

• Product: https://github.com/oauthlib/oauthlib/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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