Multiple components in Apache NiFi 0.0.1 to 1.16.0 do not restrict XML External Entity references in the default configuration. The Standard Content Viewer service attempts to resolve XML External Entity references when viewing formatted XML files. The following Processors attempt to resolve XML External Entity references when configured with default property values: - EvaluateXPath - EvaluateXQuery - ValidateXml Apache NiFi flow configurations that include these Processors are vulnerable to malicious XML documents that contain Document Type Declarations with XML External Entity references. The resolution disables Document Type Declarations in the default configuration for these Processors, and disallows XML External Entity resolution in standard services.
When creating or updating credentials for single-user access, Apache NiFi wrote a copy of the Login Identity Providers configuration to the operating system temporary directory. On most platforms, the operating system temporary directory has global read permissions. NiFi immediately moved the temporary file to the final configuration directory, which significantly limited the window of opportunity for access. NiFi 1.16.0 includes updates to replace the Login Identity Providers configuration without writing a file to the operating system temporary directory.