Removed CBC ciphers to address CVE-2013-0169 (LUCKY13)

Details:

* This change removes the following CBC ciphers from the default set
  of ciphers in order to address CVE-2013-0169 (LUCKY13):
  - ECDHE-ECDSA-AES256-SHA384
  - ECDHE-RSA-AES256-SHA384
  - ECDHE-ECDSA-AES128-SHA256
  - ECDHE-RSA-AES128-SHA256
  This is done by listing them in the code, i.e. without any way to
  configure that by the user.

Signed-off-by: Andreas Maier <[email protected]>

prometheus_client/exposition.py

@@ -170,6 +170,22 @@ def _get_ssl_ctx(
     """Load context supports SSL."""
     ssl_cxt = ssl.SSLContext(protocol=protocol)
 
+    # The following chipers will be removed if the default cipher set contains
+    # them. The reason for each cipher is stated in the comment.
+    remove_cipher_names = [
+        "ECDHE-ECDSA-AES256-SHA384",  # is a CBC cipher (CVE-2013-0169)
+        "ECDHE-RSA-AES256-SHA384",    # is a CBC cipher (CVE-2013-0169)
+        "ECDHE-ECDSA-AES128-SHA256",  # is a CBC cipher (CVE-2013-0169)
+        "ECDHE-RSA-AES128-SHA256",    # is a CBC cipher (CVE-2013-0169)
+    ]
+    cipher_names = [c['name'] for c in ssl_cxt.get_ciphers()]
+    for cipher_name in remove_cipher_names:
+        try:
+            cipher_names.remove(cipher_name)
+        except ValueError:
+            pass
+    ssl_cxt.set_ciphers(':'.join(cipher_names))
+
     if cafile is not None or capath is not None:
         try:
             ssl_cxt.load_verify_locations(cafile, capath)