Prevent command injection through _.template's variable option

Closes #5085.

lodash.js

@@ -19,7 +19,8 @@
 
   /** Error message constants. */
   var CORE_ERROR_TEXT = 'Unsupported core-js use. Try https://npms.io/search?q=ponyfill.',
-      FUNC_ERROR_TEXT = 'Expected a function';
+      FUNC_ERROR_TEXT = 'Expected a function',
+      INVALID_TEMPL_VAR_ERROR_TEXT = 'Invalid `variable` option passed into `_.template`';
 
   /** Used to stand-in for `undefined` hash values. */
   var HASH_UNDEFINED = '__lodash_hash_undefined__';
@@ -165,6 +166,18 @@
   /** Used to match words composed of alphanumeric characters. */
   var reAsciiWord = /[^\x00-\x2f\x3a-\x40\x5b-\x60\x7b-\x7f]+/g;
 
+  /**
+   * Used to validate the `validate` option in `_.template` variable.
+   *
+   * Forbids characters which could potentially change the meaning of the function argument definition:
+   * - "()," (modification of function parameters)
+   * - "=" (default value)
+   * - "[]{}" (destructuring of function parameters)
+   * - "/" (beginning of a comment)
+   * - whitespace
+   */
+  var reForbiddenIdentifierChars = /[()=,{}\[\]\/\s]/;
+
   /** Used to match backslashes in property paths. */
   var reEscapeChar = /\\(\\)?/g;
 
@@ -14866,6 +14879,12 @@
       if (!variable) {
         source = 'with (obj) {\n' + source + '\n}\n';
       }
+      // Throw an error if a forbidden character was found in `variable`, to prevent
+      // potential command injection attacks.
+      else if (reForbiddenIdentifierChars.test(variable)) {
+        throw new Error(INVALID_TEMPL_VAR_ERROR_TEXT);
+      }
+
       // Cleanup code by stripping empty strings.
       source = (isEvaluating ? source.replace(reEmptyStringLeading, '') : source)
         .replace(reEmptyStringMiddle, '$1')

test/test.js

@@ -22296,6 +22296,14 @@
       }
     });
 
+    QUnit.test('should forbid code injection through the "variable" options', function(assert) {
+      assert.expect(1);
+
+      assert.raises(function () {
+        _.template('', { 'variable': '){console.log(process.env)}; with(obj' });
+      });
+    });
+
     QUnit.test('should support custom delimiters', function(assert) {
       assert.expect(2);