JDR hangs when trying to load the DTD from an external location

Issue

We are seeing a hang when executing jdr.sh, with the following thread dump:

"management-handler-thread - 1" #142 prio=5 os_prio=0 tid=0x000055dced591000 nid=0x821b waiting on condition [0x00007f55696fb000]
   java.lang.Thread.State: RUNNABLE
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
    - locked <0x00000000ed858878> (a java.net.SocksSocketImpl)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:607)
    at java.net.Socket.connect(Socket.java:556)
    at sun.net.NetworkClient.doConnect(NetworkClient.java:180)
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:465)
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:560)
    - locked <0x00000000ed853ab8> (a sun.net.www.http.HttpClient)
    at sun.net.www.http.HttpClient.<init>(HttpClient.java:244)
    at sun.net.www.http.HttpClient.New(HttpClient.java:341)
    at sun.net.www.http.HttpClient.New(HttpClient.java:359)
    at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1243)
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1177)
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1071)
    at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:1005)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1587)
    - locked <0x00000000ed8186b8> (a sun.net.www.protocol.http.HttpURLConnection)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1515)
    - locked <0x00000000ed8186b8> (a sun.net.www.protocol.http.HttpURLConnection)
    at org.apache.xerces.impl.XMLEntityManager.setupCurrentEntity(XMLEntityManager.java:1033)
    at org.apache.xerces.impl.XMLEntityManager.startEntity(XMLEntityManager.java:941)
    at org.apache.xerces.impl.XMLEntityManager.startDTDEntity(XMLEntityManager.java:908)
    at org.apache.xerces.impl.XMLDTDScannerImpl.setInputSource(XMLDTDScannerImpl.java:241)
    at org.apache.xerces.impl.XMLDocumentScannerImpl$DTDDispatcher.dispatch(XMLDocumentScannerImpl.java:1001)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:324)
    at org.apache.xerces.parsers.XML11Configuration.parse(XML11Configuration.java:875)
    at org.apache.xerces.parsers.XML11Configuration.parse(XML11Configuration.java:798)
    at org.apache.xerces.parsers.XMLParser.parse(XMLParser.java:108)
    at org.apache.xerces.parsers.DOMParser.parse(DOMParser.java:230)
    at org.apache.xerces.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:298)
    at javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:121)
    at org.jboss.as.jdr.util.XMLSanitizer.sanitize(XMLSanitizer.java:75)
    at org.jboss.as.jdr.commands.CollectFiles.execute(CollectFiles.java:109)
    at org.jboss.as.jdr.JdrRunner.collect(JdrRunner.java:130)
    at org.jboss.as.jdr.JdrReportService.collect(JdrReportService.java:95)
    at org.jboss.as.jdr.JdrReportRequestHandler$1.execute(JdrReportRequestHandler.java:74)