Fix jashkenas#2911

modules/template.js

@@ -24,6 +24,13 @@ function escapeChar(match) {
   return '\\' + escapes[match];
 }
 
+// In order to prevent third-party code injection through
+// `_.templateSettings.variable`, we test it against the following regular
+// expression. It is intentionally a bit more liberal than just matching valid
+// identifiers, but still prevents possible loopholes through defaults or
+// destructuring assignment.
+var bareIdentifier = /^\s*(\w|\$)+\s*$/;
+
 // JavaScript micro-templating, similar to John Resig's implementation.
 // Underscore templating handles arbitrary delimiters, preserves whitespace,
 // and correctly escapes quotes within interpolated code.
@@ -59,16 +66,25 @@ export default function template(text, settings, oldSettings) {
   });
   source += "';\n";
 
-  // If a variable is not specified, place data values in local scope.
-  if (!settings.variable) source = 'with(obj||{}){\n' + source + '}\n';
+  var argument = settings.variable;
+  if (argument) {
+    // Insure against third-party code injection.
+    if (!bareIdentifier.test(argument)) throw new Error(
+      'variable is not a bare identifier: ' + argument
+    );
+  } else {
+    // If a variable is not specified, place data values in local scope.
+    source = 'with(obj||{}){\n' + source + '}\n';
+    argument = 'obj';
+  }
 
   source = "var __t,__p='',__j=Array.prototype.join," +
     "print=function(){__p+=__j.call(arguments,'');};\n" +
     source + 'return __p;\n';
 
   var render;
   try {
-    render = new Function(settings.variable || 'obj', '_', source);
+    render = new Function(argument, '_', source);
   } catch (e) {
     e.source = source;
     throw e;
@@ -79,7 +95,6 @@ export default function template(text, settings, oldSettings) {
   };
 
   // Provide the compiled source as a convenience for precompilation.
-  var argument = settings.variable || 'obj';
   template.source = 'function(' + argument + '){\n' + source + '}';
 
   return template;