Python: Port ReflectedXss query (and tests)

python/ql/src/experimental/Security-new-dataflow/CWE-079/ReflectedXss.ql

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+/**
+ * @name Reflected server-side cross-site scripting
+ * @description Writing user input directly to a web page
+ *              allows for a cross-site scripting vulnerability.
+ * @kind path-problem
+ * @problem.severity error
+ * @sub-severity high
+ * @precision high
+ * @id py/reflective-xss
+ * @tags security
+ *       external/cwe/cwe-079
+ *       external/cwe/cwe-116
+ */
+
+import python
+import experimental.dataflow.DataFlow
+import experimental.dataflow.TaintTracking
+import experimental.semmle.python.Concepts
+import experimental.dataflow.RemoteFlowSources
+import DataFlow::PathGraph
+
+class ReflectedXssConfiguration extends TaintTracking::Configuration {
+  ReflectedXssConfiguration() { this = "ReflectedXssConfiguration" }
+
+  override predicate isSource(DataFlow::Node source) { source instanceof RemoteFlowSource }
+
+  override predicate isSink(DataFlow::Node sink) {
+    exists(HTTP::Server::HttpResponse response |
+      response.getContentType().toLowerCase().matches("text/html%") and
+      sink = response.getBody()
+    )
+  }
+}
+
+from ReflectedXssConfiguration config, DataFlow::PathNode source, DataFlow::PathNode sink
+where config.hasFlowPath(source, sink)
+select sink.getNode(), source, sink, "Cross-site scripting vulnerability due to $@.",
+  source.getNode(), "a user-provided value"

python/ql/test/experimental/query-tests/Security-new-dataflow/CWE-079/ReflectedXss.expected

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+edges
+nodes
+#select

python/ql/test/experimental/query-tests/Security-new-dataflow/CWE-079/ReflectedXss.qlref

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+experimental/Security-new-dataflow/CWE-079/ReflectedXss.ql

python/ql/test/experimental/query-tests/Security-new-dataflow/CWE-079/reflected_xss.py

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+from flask import Flask, request, make_response, escape
+
+app = Flask(__name__)
+
+@app.route('/unsafe')
+def unsafe():
+    first_name = request.args.get('name', '')
+    return make_response("Your name is " + first_name)
+
+@app.route('/safe')
+def safe():
+    first_name = request.args.get('name', '')
+    return make_response("Your name is " + escape(first_name))