The HL7 FHIR IG publisher is a tool to take a set of inputs and create a standard FHIR IG. Prior to version 1.7.4, XSLT transforms performed by various components are vulnerable to XML external entity injections. A processed XML file with a malicious DTD tag ( ]> could produce XML containing data from the host system. This impacts use cases where org.hl7.fhir.publisher is being used to within a host where external clients can submit XML. A previous release provided an incomplete solution revealed by new testing. This issue has been patched as of version 1.7.4. No known workarounds are available.
The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.
XML documents optionally contain a Document Type Definition (DTD), which, among other features, enables the definition of XML entities. It is possible to define an entity by providing a substitution string in the form of a URI. The XML parser can access the contents of this URI and embed these contents back into the XML document for further processing. By submitting an XML file that defines an external entity with a file:// URI, an attacker can cause the processing application to read the contents of a local file. For example, a URI such as “file:///c:/winnt/win.ini” designates (in Windows) the file C:\Winnt\win.ini, or file:///etc/passwd designates the password file in Unix-based systems. Using URIs with other schemes such as http://, the attacker can force the application to make outgoing requests to servers that the attacker cannot reach directly, which can be used to bypass firewall restrictions or hide the source of attacks such as port scanning. Once the content of the URI is read, it is fed back into the application that is processing the XML. This application may echo back the data (e.g. in an error message), thereby exposing the file contents.