HttpUtils#getURLConnection method disables explicitly hostname verification for HTTPS connections making clients vulnerable to man-in-the-middle attacks. Calcite uses internally this method to connect with Druid and Splunk so information leakage may happen when using the respective Calcite adapters. The method itself is in a utility class so people may use it to create vulnerable HTTPS connections for other applications. From Apache Calcite 1.26 onwards, the hostname verification will be performed using the default JVM truststore.

Apache Calcite 1.22.0 introduced the SQL operators EXISTS_NODE, EXTRACT_XML, XML_TRANSFORM and EXTRACT_VALUE do not restrict XML External Entity references in their configuration, making them vulnerable to a potential XML External Entity (XXE) attack. Therefore any client exposing these operators, typically by using Oracle dialect (the first three) or MySQL dialect (the last one), is affected by this vulnerability (the extent of it will depend on the user under which the application is running). From Apache Calcite 1.32.0 onwards, Document Type Declarations and XML External Entity resolution are disabled on the impacted operators.

Apache Calcite Avatica JDBC driver creates HTTP client instances based on class names provided via `httpclient_impl` connection property; however, the driver does not verify if the class implements the expected interface before instantiating it, which can lead to code execution loaded via arbitrary classes and in rare cases remote code execution. To exploit the vulnerability: 1) the attacker needs to have privileges to control JDBC connection parameters; 2) and there should be a vulnerable class (constructor with URL parameter and ability to execute code) in the classpath. From Apache Calcite Avatica 1.22.0 onwards, it will be verified that the class implements the expected interface before invoking its constructor.