WsgiDAV: Blind SQL injection in the MySQL provider

WsgiDAV is a generic and extendable WebDAV server based on WSGI. Prior to 4.3.5, the sample MySQLBrowserProvider in wsgidav/samples/mysql_dav_provider.py concatenates the record key parsed from a request URL directly into SQL WHERE clauses. The affected _exists_record_by_primary_key, _get_field_by_primary_key, and _get_record_by_primary_key methods are part of a shipped example provider that is not enabled by default. An attacker who can access a share explicitly configured with this non-default provider can inject SQL through a normal GET request; anonymously exposed read shares permit a status-code oracle and extraction of arbitrary data reachable by the configured MySQL account. This issue is fixed in version 4.3.5.