tls: command-line switch and envar cipher-list override

Add command line switches and environment variables to override
the default cipher suite in tls.js

`--cipher-list` and `NODE_CIPHER_LIST` can be used to completely
override the default cipher list with a given value.

`--enable-legacy-cipher-list` and `NODE_LEGACY_CIPHER_LIST` can
be used to reset the default cipher list back to a known legacy
value shipped in prior Node.js releases

A new `getLegacyCiphers` method on the tis module allows
programmatic access to the old cipher list defaults.

Author: jasnell

doc/api/tls.markdown

@@ -136,6 +136,81 @@ the character "E" appended to the traditional abbreviations):
 Ephemeral methods may have some performance drawbacks, because key generation
 is expensive.
 
+## Modifying the Default Cipher Suite
+
+Node.js is built with a default suite of enabled and disabled ciphers.
+Currently, the default cipher suite is:
+
+    ECDHE-RSA-AES256-SHA384:DHE-RSA-AES256-SHA384:ECDHE-RSA-AES256-SHA256:
+    DHE-RSA-AES256-SHA256:ECDHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA256:
+    HIGH:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!SRP:!CAMELLIA
+
+This default can be overridden entirely using the `--cipher-list` command line
+switch or `NODE_CIPHER_LIST` environment variable. For instance:
+
+    node --cipher-list=ECDHE-RSA-AES256-SHA384:DHE-RSA-AES256-SHA384
+
+Setting the environment variable would have the same effect:
+
+    NODE_CIPHER_LIST=ECDHE-RSA-AES256-SHA384:DHE-RSA-AES256-SHA384
+
+CAUTION: The default cipher suite has been carefully selected to reflect current
+security best practices and risk mitigation. Changing the default cipher suite
+can have a significant impact on the security of an application. The
+`--cipher-list` and `NODE_CIPHER_LIST` options should only be used if
+absolutely necessary.
+
+### Using Legacy Default Cipher Suite ###
+
+It is possible for the built-in default cipher suite to change from one release
+of Node.js to another. For instance, v0.10.38 uses a different default than
+v0.12.2. Such changes can cause issues with applications written to assume
+certain specific defaults. To help buffer applications against such changes,
+the `--enable-legacy-cipher-list` command line switch or `NODE_LEGACY_CIPHER_LIST`
+environment variable can be set to specify a specific preset default:
+
+    # Use the v0.10.38 defaults
+    node --enable-legacy-cipher-list=v0.10.38
+    // or
+    NODE_LEGACY_CIPHER_LIST=v0.10.38
+
+    # Use the v0.12.2 defaults
+    node --enable-legacy-cipher-list=v0.12.2
+    // or
+    NODE_LEGACY_CIPHER_LIST=v0.12.2
+
+Currently, the values supported for the `enable-legacy-cipher-list` switch and
+`NODE_LEGACY_CIPHER_LIST` environment variable include:
+
+    v0.10.38 - To enable the default cipher suite used in v0.10.38
+
+      ECDHE-RSA-AES128-SHA256:AES128-GCM-SHA256:RC4:HIGH:!MD5:!aNULL:!EDH
+
+    v0.10.39 - To enable the default cipher suite used in v0.10.39
+
+      ECDHE-RSA-AES128-SHA256:AES128-GCM-SHA256:HIGH:!RC4:!MD5:!aNULL:!EDH
+
+    v0.12.2 - To enable the default cipher suite used in v0.12.2
+
+      ECDHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA256:AES128-GCM-SHA256:RC4:
+      HIGH:!MD5:!aNULL
+
+    v.0.12.3 - To enable the default cipher suite used in v0.12.3
+
+      ECDHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA256:AES128-GCM-SHA256:HIGH:
+      !RC4:!MD5:!aNULL
+
+These legacy cipher suites are also made available for use via the
+`getLegacyCiphers()` method:
+
+    var tls = require('tls');
+    console.log(tls.getLegacyCiphers('v0.10.38'));
+
+CAUTION: Changes to the default cipher suite are typically made in order to
+strengthen the default security for applications running within Node.js.
+Reverting back to the defaults used by older releases can weaken the security
+of your applications. The legacy cipher suites should only be used if absolutely
+necessary.
 
 ## tls.getCiphers()
 
@@ -146,6 +221,12 @@ Example:
     var ciphers = tls.getCiphers();
     console.log(ciphers); // ['AES128-SHA', 'AES256-SHA', ...]
 
+## tls.getLegacyCiphers(version)
+
+Returns the legacy default cipher suite for the specified Node.js release.
+
+Example:
+    var cipher_suite = tls.getLegacyCiphers('v0.10.38');
 
 ## tls.createServer(options[, secureConnectionListener])
 

lib/tls.js

@@ -21,6 +21,8 @@
 
 'use strict';
 
+var _crypto = process.binding('crypto');
+
 var net = require('net');
 var url = require('url');
 var util = require('util');
@@ -35,29 +37,14 @@ exports.CLIENT_RENEG_WINDOW = 600;
 
 exports.SLAB_BUFFER_SIZE = 10 * 1024 * 1024;
 
-exports.DEFAULT_CIPHERS = [
-  'ECDHE-RSA-AES256-SHA384',
-  'DHE-RSA-AES256-SHA384',
-  'ECDHE-RSA-AES256-SHA256',
-  'DHE-RSA-AES256-SHA256',
-  'ECDHE-RSA-AES128-SHA256',
-  'DHE-RSA-AES128-SHA256',
-  'HIGH',
-  '!aNULL',
-  '!eNULL',
-  '!EXPORT',
-  '!DES',
-  '!RC4',
-  '!MD5',
-  '!PSK',
-  '!SRP',
-  '!CAMELLIA'
-].join(':');
+exports.DEFAULT_CIPHERS = _crypto.DEFAULT_CIPHER_LIST;
 
 exports.DEFAULT_ECDH_CURVE = 'prime256v1';
 
+exports.getLegacyCiphers = _crypto.getLegacyCiphers;
+
 exports.getCiphers = function() {
-  var names = process.binding('crypto').getSSLCiphers();
+  var names = _crypto.getSSLCiphers();
   // Drop all-caps names in favor of their lowercase aliases,
   var ctx = {};
   names.forEach(function(name) {

src/node.cc

@@ -2929,6 +2929,12 @@ static void PrintHelp() {
 #endif
          "  --enable-ssl2        enable ssl2\n"
          "  --enable-ssl3        enable ssl3\n"
+         "  --cipher-list=val    specify the default TLS cipher list\n"
+         "  --enable-legacy-cipher-list=val \n"
+         "                       set to v0.10.38 to use the v0.10.38 list,\n"
+         "                       set to v0.10.39 to use the v0.10.39 list.\n"
+         "                       set to v0.12.2 to use the v0.12.2 list.\n"
+         "                       set to v0.12.3 to use the v0.12.3 list.\n"
          "\n"
          "Environment variables:\n"
 #ifdef _WIN32
@@ -2946,6 +2952,12 @@ static void PrintHelp() {
          "                       (will extend linked-in data)\n"
 #endif
 #endif
+         "NODE_CIPHER_LIST       Override the default TLS cipher list\n"
+         "NODE_LEGACY_CIPHER_LIST\n"
+         "                       Set to v0.10.38 to use the v0.10.38 list,\n"
+         "                       Set to v0.10.39 to use the v0.10.39 list.\n"
+         "                       Set to v0.12.2 to use the v0.12.2 list.\n"
+         "                       Set to v0.12.3 to use the v0.12.3 list.\n"
          "\n"
          "Documentation can be found at http://nodejs.org/\n");
 }
@@ -2985,6 +2997,7 @@ static void ParseArgs(int* argc,
   unsigned int new_argc = 1;
   new_v8_argv[0] = argv[0];
   new_argv[0] = argv[0];
+  bool using_legacy_cipher_list = FALSE;
 
   unsigned int index = 1;
   while (index < nargs && argv[index][0] == '-') {
@@ -3040,6 +3053,17 @@ static void ParseArgs(int* argc,
     } else if (strcmp(arg, "--v8-options") == 0) {
       new_v8_argv[new_v8_argc] = "--help";
       new_v8_argc += 1;
+    } else if (strncmp(arg, "--cipher-list=", 14) == 0) {
+      if (!using_legacy_cipher_list) {
+        DEFAULT_CIPHER_LIST = arg + 14;
+      }
+    } else if (strncmp(arg, "--enable-legacy-cipher-list=", 28) == 0) {
+      using_legacy_cipher_list = true;
+      // use the original v0.10.x/v0.12.x cipher lists
+      const char * legacy_list = legacy_cipher_list(arg+28);
+      if (legacy_list != NULL) {
+        DEFAULT_CIPHER_LIST = legacy_list;
+      }
 #if defined(NODE_HAVE_I18N_SUPPORT)
     } else if (strncmp(arg, "--icu-data-dir=", 15) == 0) {
       icu_data_dir = arg + 15;
@@ -3402,6 +3426,23 @@ void Init(int* argc,
     }
   }
 
+  // if parseargs didn't come up with a cipher_list,
+  // try the NODE_CIPHER_LIST env variable to grab the
+  // list.
+  const char * cipher_list = getenv("NODE_CIPHER_LIST");
+  if (cipher_list != NULL) {
+    DEFAULT_CIPHER_LIST = cipher_list;
+  }
+  // Allow the NODE_LEGACY_CIPHER_LIST envar to override the other
+  // cipher list options. NODE_LEGACY_CIPHER_LIST=v0.10.x will use
+  // the cipher list from v0.10.x, NODE_LEGACY_CIPHER_LIST=v0.12.x will
+  // use the cipher list from v0.12.x
+  const char * leg_cipher_list =
+    legacy_cipher_list(getenv("NODE_LEGACY_CIPHER_LIST"));
+  if (leg_cipher_list != NULL) {
+    DEFAULT_CIPHER_LIST = leg_cipher_list;
+  }
+
 #if defined(NODE_HAVE_I18N_SUPPORT)
   if (icu_data_dir == NULL) {
     // if the parameter isn't given, use the env variable.

src/node.h

@@ -223,6 +223,18 @@ NODE_EXTERN void RunAtExit(Environment* env);
   }                                                                           \
   while (0)
 
+#define NODE_DEFINE_STRING_CONSTANT(target, constant)                         \
+  do {                                                                        \
+    v8::Isolate* isolate = v8::Isolate::GetCurrent();                         \
+    v8::Local<v8::String> constant_name =                                     \
+        v8::String::NewFromUtf8(isolate, #constant);                          \
+    v8::Local<v8::String> constant_value =                                    \
+        v8::String::NewFromUtf8(isolate, constant);                           \
+    v8::PropertyAttribute constant_attributes =                               \
+        static_cast<v8::PropertyAttribute>(v8::ReadOnly | v8::DontDelete);    \
+    (target)->ForceSet(constant_name, constant_value, constant_attributes);   \
+  } while (0)
+
 // Used to be a macro, hence the uppercase name.
 template <typename TypeName>
 inline void NODE_SET_METHOD(const TypeName& recv,

src/node_crypto.cc

@@ -77,6 +77,7 @@ namespace node {
 
 bool SSL2_ENABLE = false;
 bool SSL3_ENABLE = false;
+const char * DEFAULT_CIPHER_LIST = DEFAULT_CIPHER_LIST_HEAD;
 
 namespace crypto {
 
@@ -4851,6 +4852,26 @@ static void array_push_back(const TypeName* md,
   ctx->arr->Set(ctx->arr->Length(), OneByteString(ctx->env()->isolate(), from));
 }
 
+// borrowed from v8
+// (see http://v8.googlecode.com/svn/trunk/samples/shell.cc)
+const char* ToCString(const String::Utf8Value& value) {
+  return *value ? *value : "<string conversion failed>";
+}
+
+void DefaultCiphers(const v8::FunctionCallbackInfo<v8::Value>& args) {
+  Environment* env = Environment::GetCurrent(args.GetIsolate());
+  HandleScope scope(env->isolate());
+  v8::String::Utf8Value key(args[0]);
+  const char * list = legacy_cipher_list(ToCString(key));
+  if (list != NULL) {
+    args.GetReturnValue().Set(
+      v8::String::NewFromUtf8(args.GetIsolate(), list));
+  } else {
+    args.GetReturnValue().Set(
+      v8::String::NewFromUtf8(args.GetIsolate(),
+                             DEFAULT_CIPHER_LIST_HEAD));
+  }
+}
 
 void GetCiphers(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args.GetIsolate());
@@ -5171,6 +5192,8 @@ void InitCrypto(Handle<Object> target,
 
   NODE_DEFINE_CONSTANT(target, SSL3_ENABLE);
   NODE_DEFINE_CONSTANT(target, SSL2_ENABLE);
+  NODE_DEFINE_STRING_CONSTANT(target, DEFAULT_CIPHER_LIST);
+  NODE_SET_METHOD(target, "getLegacyCiphers", DefaultCiphers);
 }
 
 }  // namespace crypto

src/node_crypto.h

@@ -38,6 +38,7 @@
 
 #include "v8.h"
 
+#include <string.h>
 #include <openssl/ssl.h>
 #include <openssl/ec.h>
 #include <openssl/ecdh.h>
@@ -59,10 +60,51 @@
 # define NODE__HAVE_TLSEXT_STATUS_CB
 #endif  // !defined(OPENSSL_NO_TLSEXT) && defined(SSL_CTX_set_tlsext_status_cb)
 
+#define DEFAULT_CIPHER_LIST_V10_38 "ECDHE-RSA-AES128-SHA256:"                  \
+                                "AES128-GCM-SHA256:RC4:HIGH:!MD5:!aNULL:!EDH"
+
+#define DEFAULT_CIPHER_LIST_V10_39 "ECDHE-RSA-AES128-SHA256:"                  \
+                                "AES128-GCM-SHA256:HIGH:!RC4:!MD5:!aNULL:!EDH"
+
+#define DEFAULT_CIPHER_LIST_V12_2 "ECDHE-RSA-AES128-SHA256:"                   \
+                                "DHE-RSA-AES128-SHA256:AES128-GCM-SHA256:RC4:" \
+                                "HIGH:!MD5:!aNULL"
+
+#define DEFAULT_CIPHER_LIST_V12_3  "ECDHE-RSA-AES128-SHA256:"                  \
+                                "DHE-RSA-AES128-SHA256:AES128-GCM-SHA256:HIGH:"\
+                                "!RC4:!MD5:!aNULL"
+
+#define DEFAULT_CIPHER_LIST_HEAD "ECDHE-RSA-AES256-SHA384:"                   \
+                                 "DHE-RSA-AES256-SHA384:"                     \
+                                 "ECDHE-RSA-AES256-SHA256:"                   \
+                                 "DHE-RSA-AES256-SHA256:"                     \
+                                 "ECDHE-RSA-AES128-SHA256:"                   \
+                                 "DHE-RSA-AES128-SHA256:"                     \
+                                 "HIGH:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:" \
+                                 "!PSK:!SRP:!CAMELLIA"
+
+static inline const char * legacy_cipher_list(const char * ver) {
+  if (ver == NULL) {
+    return NULL;
+  }
+  if (strncmp(ver, "v0.10.38", 8) == 0) {
+    return DEFAULT_CIPHER_LIST_V10_38;
+  } else if (strncmp(ver, "v0.10.39", 8) == 0) {
+    return DEFAULT_CIPHER_LIST_V10_39;
+  } else if (strncmp(ver, "v0.12.2", 7) == 0) {
+    return DEFAULT_CIPHER_LIST_V12_2;
+  } else if (strncmp(ver, "v0.12.3", 7) == 0) {
+    return DEFAULT_CIPHER_LIST_V12_3;
+  } else {
+    return NULL;
+  }
+}
+
 namespace node {
 
 extern bool SSL2_ENABLE;
 extern bool SSL3_ENABLE;
+extern const char * DEFAULT_CIPHER_LIST;
 
 namespace crypto {