The vulnerability arises in utcp-http before 1.1.4, where the library does not validate the OAuth2 tokenUrl supplied in a remote OpenAPI specification. An attacker can supply a malicious spec that directs the library to send a victim’s client_id and client_secret to an arbitrary endpoint. The attacker then receives those credentials, enabling credential theft and potential impersonation. This flaw falls under CWE‑918 due to insecure input validation of the tokenUrl parameter.

All installations of the universal-tool-calling-protocol python-utcp package with utcp-http versions earlier than 1.1.4 are affected. The vulnerability exists wherever an untrusted OpenAPI specification is loaded and the generated OAuth2‑protected tool is invoked. No specific operating system or platform restrictions are reported.

The CVSS score for this issue is 7.1, indicating moderate severity with the potential for significant impact if exploited. The EPSS score is not provided, and the vulnerability is not listed in CISA’s KEV catalog. The likely attack vector is remote; an attacker only needs to convince a user to load an attacker‑controlled OpenAPI spec, then configure the tool to perform an OAuth2 flow. If successful, the attacker learns valid client credentials and can impersonate or further compromise the victim’s services.