An unauthenticated OAuth2 token refresh endpoint runs without any access control and sends a POST request to the credential‑controlled accessTokenUrl on the server’s behalf. The request includes sensitive information such as client_id, client_secret, grant_type, and refresh_token, and the full response body is returned to the caller. This flaw matches the weakness identified by CWE‑639 and enables an attacker to cause the server to contact an arbitrary endpoint and exfiltrate authentication secrets, leading to compromise of downstream services and data exposure.

The Vulnerability affects FlowiseAI’s Flowise application in all releases prior to version 3.1.3. Versions 3.1.3 and later have an authentication requirement for the refresh operation and SSRF controls in place.

The CVSS score of 8.5 indicates a high‑severity condition. The vulnerability is publicly known but is not listed in the CISA KEV catalog and no EPSS score is available, implying limited public exploitation data. Attackers need only trigger the endpoint (which is reachable without authentication) and host a server to receive the outbound POST requests. With the supplied credentials reflected in the response, an attacker can capture client‑secret values and elevate privileges within the application or its integrations. The attack surface is wide, affecting any deployment where the refresh endpoint remains public.