Check for RSA exponent of 1, resulting in F score

CHANGELOG

@@ -1,5 +1,8 @@
 # Nmap Changelog ($Id$); -*-text-*-
 
+o [NSE] ssl-enum-ciphers will give a failing score to any server with an RSA
+  certificate whose public key uses an exponent of 1. [Daniel Miller]
+
 o Update oldest supported Windows version to Vista (Windows 6.0). This enables
   the use of the poll Nsock engine. [Daniel Miller]
 

nselib/nmap.luadoc

@@ -734,7 +734,7 @@ function pcap_close()
 --
 -- If the <code>pubkey</code> is type <code>"rsa"</code>, it will also have an
 -- <code>exponent</code> member, containing the public exponent as a bignum. If
--- the type is <code>"ec"</code>, it will have an <code>ecdhparams</code>
+-- the type is <code>"ec"</code>, it will have an <code>ecdhparams.curve_params</code>
 -- member, containing a table with <code>ec_curve_type</code> and
 -- <code>curve</code> keys as strings.
 --

scripts/ssl-enum-ciphers.nse

@@ -322,7 +322,7 @@ categories = {"discovery", "intrusive"}
 -- http://seclists.org/nmap-dev/2012/q3/156
 -- http://seclists.org/nmap-dev/2010/q1/859
 local CHUNK_SIZE = 64
-local have_ssl, _ = pcall(require,'openssl')
+local have_ssl, openssl = pcall(require,'openssl')
 
 -- Add additional context (protocol) to debug output
 local function ctx_log(level, protocol, fmt, ...)
@@ -715,6 +715,12 @@ local function find_ciphers_group(host, port, protocol, group, scores)
                       scores.warnings["Weak certificate signature: SHA1"] = true
                     end
                     kex_strength = tls.rsa_equiv(kex.pubkey, c.pubkey.bits)
+                    if c.pubkey.exponent then
+                      if openssl.bignum_bn2dec(c.pubkey.exponent) == "1" then
+                        kex_strength = 0
+                        scores.warnings["Certificate RSA exponent is 1, score capped at F"] = true
+                      end
+                    end
                     if c.pubkey.ecdhparams then
                       if c.pubkey.ecdhparams.curve_params.ec_curve_type == "namedcurve" then
                         extra = c.pubkey.ecdhparams.curve_params.curve
@@ -747,6 +753,10 @@ local function find_ciphers_group(host, port, protocol, group, scores)
                     extra = string.format("%s %d", kex.type, kex_info.strength)
                   end
                 end
+                if kex_info.rsa and kex_info.rsa.exponent == 1 then
+                  kex_strength = 0
+                  scores.warnings["Certificate RSA exponent is 1, score capped at F"] = true
+                end
               end
             end
             scores[name] = {