Support fragmented TLS records. Closes #194

CHANGELOG

@@ -1,5 +1,8 @@
 # Nmap Changelog ($Id$); -*-text-*-
 
+o [NSE] [GH#194] Add support for reading fragmented TLS messages to
+  ssl-enum-ciphers. [Jacob Gajek]
+
 o [Ncat] [GH#193] Fix Ncat listen mode over Unix sockets (named pipes) on OS X.
   This was crashing with the error:
     Ncat: getnameinfo failed: Undefined error: 0 QUITTING.

nselib/tls.lua

@@ -1108,12 +1108,14 @@ end
 
 ---
 -- Read a SSL/TLS record
--- @param buffer The read buffer
+-- @param buffer   The read buffer
--- @param i      The position in the buffer to start reading
+-- @param i        The position in the buffer to start reading
+-- @param fragment Message fragment left over from previous record (nil if none)
 -- @return The current position in the buffer
 -- @return The record that was read, as a table
-function record_read(buffer, i)
+function record_read(buffer, i, fragment)
   local b, h, len
+  local add = 0
 
   ------------
   -- Header --
@@ -1148,6 +1150,14 @@ function record_read(buffer, i)
     return i, nil
   end
 
+  -- Adjust buffer and length to account for message fragment left over
+  -- from last record.
+  if fragment then
+    add = #fragment
+    len = len + add
+    buffer = buffer:sub(1, j - 1) .. fragment .. buffer:sub(j, -1)
+  end
+
   -- Convert to human-readable form.
 
   ----------
@@ -1155,12 +1165,11 @@ function record_read(buffer, i)
   ----------
 
   h["body"] = {}
-  while j < len do
+
+  while j <= len do
     -- RFC 2246, 6.2.1 "multiple client messages of the same ContentType may
     -- be coalesced into a single TLSPlaintext record"
-    -- TODO: implement reading of fragmented records
     b = {}
-    table.insert(h["body"], b)
     if h["type"] == "alert" then
       -- Parse body.
       j, b["level"] = bin.unpack("C", buffer, j)
@@ -1169,7 +1178,16 @@ function record_read(buffer, i)
       -- Convert to human-readable form.
       b["level"] = find_key(TLS_ALERT_LEVELS, b["level"])
       b["description"] = find_key(TLS_ALERT_REGISTRY, b["description"])
+
+      table.insert(h["body"], b)
     elseif h["type"] == "handshake" then
+
+      -- Check for message fragmentation.
+      if len - j < 3 then
+        h.fragment = buffer:sub(j, len)
+        return len + 1 - add, h
+      end
+
       -- Parse body.
       j, b["type"] = bin.unpack("C", buffer, j)
       local msg_end
@@ -1179,6 +1197,12 @@ function record_read(buffer, i)
       -- Convert to human-readable form.
       b["type"] = find_key(TLS_HANDSHAKETYPE_REGISTRY, b["type"])
 
+      -- Check for message fragmentation.
+      if msg_end > len + 1 then
+        h.fragment = buffer:sub(j - 4, len)
+        return len + 1 - add, h
+      end
+
       if b["type"] == "server_hello" then
         -- Parse body.
         j, b["protocol"] = bin.unpack(">S", buffer, j)
@@ -1226,18 +1250,21 @@ function record_read(buffer, i)
         stdnse.debug2("Unknown handshake message type: %s", b["type"])
         j, b["data"] = bin.unpack("A" .. msg_end - j, buffer, j)
       end
+
+      table.insert(h["body"], b)
     elseif h["type"] == "heartbeat" then
       j, b["type"], b["payload_length"] = bin.unpack("C>S", buffer, j)
       j, b["payload"], b["padding"] = bin.unpack("PP", buffer, j)
+      table.insert(h["body"], b)
     else
       stdnse.debug1("Unknown message type: %s", h["type"])
     end
   end
 
   -- Ignore unparsed bytes.
-  j = len+1
+  j = len + 1
 
-  return j, h
+  return j - add, h
 end
 
 ---

scripts/ssl-enum-ciphers.nse

@@ -149,20 +149,22 @@ end
 local function get_record_iter(sock)
   local buffer = ""
   local i = 1
+  local fragment
   return function ()
     local record
-    i, record = tls.record_read(buffer, i)
+    i, record = tls.record_read(buffer, i, fragment)
     if record == nil then
       local status, err
       status, buffer, err = tls.record_buffer(sock, buffer, i)
       if not status then
         return nil, err
       end
-      i, record = tls.record_read(buffer, i)
+      i, record = tls.record_read(buffer, i, fragment)
       if record == nil then
         return nil, "done"
       end
     end
+    fragment = record.fragment
     return record
   end
 end