Merge pull request #528 from taus-semmle/python-flask-debug

Python: Implement check for flask debug mode.

change-notes/1.19/analysis-python.md

@@ -56,6 +56,7 @@ A new predicate `Stmt.getAnEntryNode()` has been added to make it easier to writ
 
 | **Query**                   | **Tags**  | **Purpose**                                                        |
 |-----------------------------|-----------|--------------------------------------------------------------------|
+| Flask app is run in debug mode (`py/flask-debug`) | security, external/cwe/cwe-215, external/cwe/cwe-489 | Finds instances where a Flask application is run in debug mode. Enabled on LGTM by default. |
 | Information exposure through an exception (`py/stack-trace-exposure`) | security, external/cwe/cwe-209, external/cwe/cwe-497 | Finds instances where information about an exception may be leaked to an external user. Enabled on LGTM by default. |
 | Request without certificate validation (`py/request-without-cert-validation`) | security, external/cwe/cwe-295 | Finds requests where certificate verification has been explicitly turned off, possibly allowing man-in-the-middle attacks. Not enabled on LGTM by default. |
 

python/ql/src/Security/CWE-215/FlaskDebug.py

@@ -0,0 +1,9 @@
+from flask import Flask
+
+app = Flask(__name__)
+
+@app.route('/crash')
+def main():
+    raise Exception()
+
+app.run(debug=True)

python/ql/src/Security/CWE-215/FlaskDebug.qhelp

@@ -0,0 +1,39 @@
+<!DOCTYPE qhelp PUBLIC
+"-//Semmle//qhelp//EN"
+"qhelp.dtd">
+<qhelp>
+     <overview>
+          <p>
+              Running a Flask application with debug mode enabled may allow an
+              attacker to gain access through the Werkzeug debugger.
+          </p>
+
+     </overview>
+     <recommendation>
+
+          <p>
+               Ensure that Flask applications that are run in a production
+               environment have debugging disabled.
+          </p>
+
+     </recommendation>
+     <example>
+
+          <p>
+            Running the following code starts a Flask webserver that has
+            debugging enabled. By visiting <code>/crash</code>, it is possible
+            to gain access to the debugger, and run arbitrary code through the
+            interactive debugger.
+          </p>
+
+          <sample src="FlaskDebug.py" />
+
+     </example>
+
+     <references>
+       <li>Flask Quickstart Documentation: <a href="http://flask.pocoo.org/docs/1.0/quickstart/#debug-mode">Debug Mode</a>.</li>
+       <li>Werkzeug Documentation: <a href="http://werkzeug.pocoo.org/docs/0.14/debug/">Debugging Applications</a>.</li>
+     </references>
+
+</qhelp>
+

python/ql/src/Security/CWE-215/FlaskDebug.ql

@@ -0,0 +1,23 @@
+/**
+ * @name Flask app is run in debug mode
+ * @description Running a Flask app in debug mode may allow an attacker to run arbitrary code through the Werkzeug debugger.
+ * @kind problem
+ * @problem.severity error
+ * @precision high
+ * @id py/flask-debug
+ * @tags security
+ *       external/cwe/cwe-215
+ *       external/cwe/cwe-489
+ */
+
+import python
+
+import semmle.python.web.flask.General
+
+
+from CallNode call, Object isTrue
+where
+    call = theFlaskClass().declaredAttribute("run").(FunctionObject).getACall() and
+    call.getArgByName("debug").refersTo(isTrue) and
+    isTrue.booleanValue() = true
+select call, "A Flask app appears to be run in debug mode. This may allow an attacker to run arbitrary code through the debugger."

python/ql/test/query-tests/Security/CWE-215/FlaskDebug.expected

@@ -0,0 +1,3 @@
+| test.py:10:1:10:19 | ControlFlowNode for Attribute() | A Flask app appears to be run in debug mode. This may allow an attacker to run arbitrary code through the debugger. |
+| test.py:25:1:25:20 | ControlFlowNode for Attribute() | A Flask app appears to be run in debug mode. This may allow an attacker to run arbitrary code through the debugger. |
+| test.py:29:1:29:20 | ControlFlowNode for Attribute() | A Flask app appears to be run in debug mode. This may allow an attacker to run arbitrary code through the debugger. |

python/ql/test/query-tests/Security/CWE-215/FlaskDebug.qlref

@@ -0,0 +1 @@
+Security/CWE-215/FlaskDebug.ql

python/ql/test/query-tests/Security/CWE-215/options

@@ -0,0 +1 @@
+semmle-extractor-options: --max-import-depth=2 -p ../lib

python/ql/test/query-tests/Security/CWE-215/test.py

@@ -0,0 +1,37 @@
+from flask import Flask
+
+app = Flask(__name__)
+
+@app.route('/crash')
+def main():
+    raise Exception()
+
+# bad
+app.run(debug=True)
+
+# okay
+app.run()
+app.run(debug=False)
+
+# also okay
+run(debug=True)
+
+app.notrun(debug=True)
+
+# a slightly more involved example using flow and truthy values
+
+DEBUG = True
+
+app.run(debug=DEBUG)
+
+DEBUG = 1
+
+app.run(debug=DEBUG)
+
+if False:
+    app.run(debug=True)
+
+# false negative
+
+runapp = app.run
+runapp(debug=True)

python/ql/test/query-tests/Security/lib/flask/__init__.py

@@ -1,7 +1,7 @@
 
 
 class Flask(object): 
-    pass
+    def run(self, *args, **kwargs): pass
 
 from .globals import request