CVE-2026-86411: curl: curl: FTP connection reuse inherits client-certificate

Severity: Critical

CVSS Score: 9.1

An `ftp://` transfer configured with `CURLUSESSL_NONE` can reuse a pooled FTP control connection that a previous easy handle upgraded with `STARTTLS` and authenticated using a client certificate. The second handle performs neither a new TLS handshake nor a new FTP login, so the server continues to authorize it under the first handle's certificate identity.