Python: Port insecure default protocol

- use API graphs
- update .qlhelp-file
- limit to versions below 3.4
- move tests to its own directory to only test on old version

python/ql/src/Security/CWE-327/InsecureDefaultProtocol.qhelp

@@ -13,7 +13,7 @@
 
           <p>
             Ensure that a modern, strong protocol is used. All versions of SSL,
-            and TLS 1.0 are known to be vulnerable to attacks. Using TLS 1.1 or
+            and TLS 1.0 and 1.1 are known to be vulnerable to attacks. Using TLS 1.2 or
             above is strongly recommended. If no explicit
             <code>ssl_version</code> is specified, the default
             <code>PROTOCOL_TLS</code> is chosen. This protocol is insecure and
@@ -34,13 +34,15 @@
           <p>
             Both of the cases above should be updated to use a secure protocol
             instead, for instance by specifying
-            <code>ssl_version=PROTOCOL_TLSv1_1</code> as a keyword argument.
+            <code>ssl_version=PROTOCOL_TLSv1_2</code> as a keyword argument.
           </p>
           <p>
             Note that <code>ssl.wrap_socket</code> has been deprecated in
             Python 3.7. A preferred alternative is to use
             <code>ssl.SSLContext</code>, which is supported in Python 2.7.9 and
-            3.2 and later versions.
+            3.2 and later versions or the convenience function
+            <code>ssl.create_default_context</code>, which is supported in Python
+            3.4 and later versions.
           </p>
      </example>
 
@@ -48,6 +50,8 @@
        <li>Wikipedia: <a href="https://en.wikipedia.org/wiki/Transport_Layer_Security"> Transport Layer Security</a>.</li>
        <li>Python 3 documentation: <a href="https://docs.python.org/3/library/ssl.html#ssl.SSLContext"> class ssl.SSLContext</a>.</li>
        <li>Python 3 documentation: <a href="https://docs.python.org/3/library/ssl.html#ssl.wrap_socket"> ssl.wrap_socket</a>.</li>
+       <li>Python 3 documentation: <a href="https://docs.python.org/3/library/ssl.html#functions-constants-and-exceptions"> notes on context creation</a>.</li>
+       <li>Python 3 documentation: <a href="https://docs.python.org/3/library/ssl.html#ssl-security"> notes on security considerations</a>.</li>
      </references>
 
 </qhelp>

python/ql/src/Security/CWE-327/InsecureDefaultProtocol.ql

@@ -11,20 +11,19 @@
  */
 
 import python
-
-FunctionValue ssl_wrap_socket() { result = Value::named("ssl.wrap_socket") }
-
-ClassValue ssl_Context_class() { result = Value::named("ssl.SSLContext") }
+import semmle.python.ApiGraphs
 
 CallNode unsafe_call(string method_name) {
-  result = ssl_wrap_socket().getACall() and
+  result = API::moduleImport("ssl").getMember("wrap_socket").getACall().asCfgNode() and
   not exists(result.getArgByName("ssl_version")) and
   method_name = "deprecated method ssl.wrap_socket"
   or
-  result = ssl_Context_class().getACall() and
+  result = API::moduleImport("ssl").getMember("SSLContext").getACall().asCfgNode() and
   not exists(result.getArgByName("protocol")) and
   not exists(result.getArg(0)) and
-  method_name = "ssl.SSLContext"
+  method_name = "ssl.SSLContext" and
+  // in version 3.4, flags were introduced to modify cotexts created with default values
+  (major_version() < 3 or minor_version() < 4)
 }
 
 from CallNode call, string method_name

python/ql/test/query-tests/Security/CWE-327/py2/InsecureProtocol.py

@@ -0,0 +1,52 @@
+import ssl
+from pyOpenSSL import SSL
+from ssl import SSLContext
+
+# true positives
+ssl.wrap_socket(ssl_version=ssl.PROTOCOL_SSLv2)
+ssl.wrap_socket(ssl_version=ssl.PROTOCOL_SSLv3)
+ssl.wrap_socket(ssl_version=ssl.PROTOCOL_TLSv1)
+
+SSLContext(protocol=ssl.PROTOCOL_SSLv2)
+SSLContext(protocol=ssl.PROTOCOL_SSLv3)
+SSLContext(protocol=ssl.PROTOCOL_TLSv1)
+
+SSL.Context(SSL.SSLv2_METHOD)
+SSL.Context(SSL.SSLv23_METHOD)
+SSL.Context(SSL.SSLv3_METHOD)
+SSL.Context(SSL.TLSv1_METHOD)
+
+# not relevant
+wrap_socket(ssl_version=ssl.PROTOCOL_SSLv3)
+wrap_socket(ssl_version=ssl.PROTOCOL_TLSv1)
+wrap_socket(ssl_version=ssl.PROTOCOL_SSLv2)
+
+Context(SSL.SSLv3_METHOD)
+Context(SSL.TLSv1_METHOD)
+Context(SSL.SSLv2_METHOD)
+Context(SSL.SSLv23_METHOD)
+
+# true positive using flow
+
+METHOD = SSL.SSLv2_METHOD
+SSL.Context(METHOD)
+
+# secure versions
+
+ssl.wrap_socket(ssl_version=ssl.PROTOCOL_TLSv1_1)
+SSLContext(protocol=ssl.PROTOCOL_TLSv1_1)
+SSL.Context(SSL.TLSv1_1_METHOD)
+
+# possibly insecure default
+ssl.wrap_socket()
+context = SSLContext()
+
+# importing the protocol constant directly
+
+from ssl import PROTOCOL_SSLv2
+
+ssl.wrap_socket(ssl_version=PROTOCOL_SSLv2)
+SSLContext(protocol=PROTOCOL_SSLv2)
+
+# FP for insecure default
+ssl.SSLContext(ssl.SSLv23_METHOD)

python/ql/test/query-tests/Security/CWE-327/py2/options

@@ -0,0 +1 @@
+semmle-extractor-options: --lang=2 -p ../lib/ --max-import-depth=3