CVE-2026-12064

When a user invokes curl using a schemeless URL combined with

`--proto-default` sftp (or scp), a disconnect occurs between the tool layer

and libcurl. The tool layer incorrectly infers the URL scheme, which

erroneously bypasses the initialization of critical SSH security options like

CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256 and CURLOPT_SSH_KNOWNHOSTS. Conversely, the

libcurl runtime successfully honors CURLOPT_DEFAULT_PROTOCOL and establishes

the connection via SFTP/SCP as specified. Because the tool layer skipped the

security configuration, these SSH host verification options are silently

omitted, causing curl to connect to an unverified SSH remote host without

throwing an error.