CVE-2026-118669

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CVE-2026-118669

Summary: OAuthLib: Token grants can use attacker-supplied client_id for authorization after authenticating a different client

Details: 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.

References: https://github.com/oauthlib/oauthlib/releases/tag/v4.0.0, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/118xxx/CVE-2026-118669.json, https://github.com/oauthlib/oauthlib/security/advisories/GHSA-7984-qgvg-3j9c, https://nvd.nist.gov/vuln/detail/CVE-2026-118669, https://github.com/oauthlib/oauthlib/commit/c951a1d09f99f14e3240973fa83c4f4287d4753d, https://github.com/oauthlib/oauthlib/pull/920