Fix: Handle ZMTP 2.0, CURVE/PLAIN, and identity padding in detection

- Add 's' flag to service probe regex (dot must match 0x0A in signature
  padding when identity length == 10)
- Remove '$' anchor from NULL probe ZMTP match to catch 2.0 responses
  longer than 10 bytes (revision + socket-type + identity frame)
- Handle partial greetings from CURVE/PLAIN servers (only 10-byte
  signature before mechanism mismatch closure)
- Tested against 19 servers: 7 NULL socket types, 2 NULL+identity,
  2 CURVE, 2 PLAIN, 6 raw ZMTP 2.0 (with/without identity)

nmap-service-probes

@@ -5277,8 +5277,11 @@ match zeo-monitor m|^ZEO monitor server version ([\w._-]+)\n.*\n\nStorage: \d+\n
 match zos-commserver m|^EZY1315E \d\d/\d\d/\d\d \d\d:\d\d:\d\d INVALID TRANID=\r\n\r\n PARTNER INET ADDR=[\d.]+ PORT=   \d+                                      | p|IBM z/OS Communications Server| o|z/OS| cpe:/o:ibm:z%2fos/
 
 # http://rfc.zeromq.org/spec:15
-# This is a backwards-compatible handshake
-match zmtp m|^\xff\0\0\0\0\0\0\0\x01\x7f$| p/ZeroMQ ZMTP 2.0/
+# ZMTP signature: 0xFF + 8 padding bytes + 0x7F. Padding may contain identity
+# length for backward compat (can be 0x0A = \n, so 's' flag is required).
+# Original match required exactly 10 bytes ($), but 2.0 servers send more
+# (revision + socket-type + identity frame). Use 's' flag for \n in padding.
+match zmtp m|^\xff.{8}\x7f|s p/ZeroMQ ZMTP/
 
 ##############################NEXT PROBE##############################
 # ZMTP 3.x (ZeroMQ Message Transport Protocol)
@@ -5291,7 +5294,8 @@ ports 41459,50051,56441,30000-65535
 
 # ZMTP response: 64-byte greeting starting with signature 0xFF...0x7F
 # Catches all ZMTP versions (2.0, 3.0, 3.1+). NSE script handles detailed parsing.
-match zmtp m|^\xff.{8}\x7f| p/ZeroMQ ZMTP/
+# 's' flag: padding bytes may contain 0x0A (\n) when identity length == 10.
+match zmtp m|^\xff.{8}\x7f|s p/ZeroMQ ZMTP/
 
 # http://www.space-walrus.com/games/Minebuilder
 # Very general, so leaving it here at the end

scripts/zmtp-info.nse

@@ -296,12 +296,13 @@ action = function(host, port)
     return nil
   end
 
-  -- Receive at least the 10-byte signature.
-  -- For ZMTP 3.x we typically get 64+ bytes, for 2.0 we get ~14 bytes.
+  -- Receive response. We ask for at least 10 bytes (the signature).
+  -- ZMTP 3.x servers typically send 64+ bytes, 2.0 servers send ~14 bytes.
+  -- CURVE/PLAIN servers may send only 10 bytes initially (partial greeting).
   local response
   status, response = socket:receive_bytes(10)
 
-  if not status or #response < 11 then
+  if not status or #response < 10 then
     socket:close()
     stdnse.debug1("No valid response received")
     return nil
@@ -317,27 +318,41 @@ action = function(host, port)
     return nil
   end
 
+  -- If we only got the 10-byte signature (partial greeting from CURVE/PLAIN
+  -- servers), try to receive more bytes for version info.
+  if #response == 10 then
+    stdnse.debug1("Got only signature (10 bytes), waiting for version...")
+    local s, more = socket:receive_bytes(1)
+    if s and more then
+      response = response .. more
+    end
+  end
+
   local output = stdnse.output_table()
   output.protocol = "ZMTP"
 
-  local major = string.byte(response, 11)
-
-  if major >= 3 then
-    -- ZMTP 3.x: ensure we have the full 64-byte greeting
-    if #response < 64 then
-      local s, more = socket:receive_bytes(64 - #response)
-      if s and more then
-        response = response .. more
-      end
-    end
-    parse_zmtp3(response, socket, output)
-  elseif major == 1 or major == 2 then
-    -- ZMTP 2.0 (revision byte 0x01) or ZMTP 2.1 (0x02)
-    parse_zmtp2(response, output)
+  if #response < 11 then
+    -- Only got the signature, no version byte. Report as ZMTP detected.
+    stdnse.debug1("ZMTP signature confirmed but no version received (%d bytes)", #response)
   else
-    -- Unknown version, report what we know
-    output.version = string.format("%d.0", major)
-    stdnse.debug1("Unknown ZMTP major version: %d", major)
+    local major = string.byte(response, 11)
+
+    if major >= 3 then
+      -- ZMTP 3.x: try to get the full 64-byte greeting
+      if #response < 64 then
+        local s, more = socket:receive_bytes(1)
+        if s and more then
+          response = response .. more
+        end
+      end
+      parse_zmtp3(response, socket, output)
+    elseif major == 1 or major == 2 then
+      -- ZMTP 2.0 (revision byte 0x01) or ZMTP 2.1 (0x02)
+      parse_zmtp2(response, output)
+    else
+      output.version = string.format("%d.0", major)
+      stdnse.debug1("Unknown ZMTP major version: %d", major)
+    end
   end
 
   socket:close()