diff --git a/CHANGELOG b/CHANGELOG
index 37ac38e..cd5bdb2 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Prevent a potential security issue for cross-site ajax requests. [Alexey Feldgendler, sam, Tobie Langel]
+
 * Test for attribute existence before applying more complex CSS3 selectors. Closes #10870. [arty, Tobie Langel]
 
 * Fix "function $A" declaration inside of a conditional (confuses IE). Closes #10882. [Jacco, Andrew Dupont]
diff --git a/src/ajax.js b/src/ajax.js
index e576a1e..a1abed6 100644
--- a/src/ajax.js
+++ b/src/ajax.js
@@ -189,7 +189,7 @@ Ajax.Request = Class.create(Ajax.Base, {
       
       var contentType = response.getHeader('Content-type');
       if (this.options.evalJS == 'force'
-          || (this.options.evalJS && contentType 
+          || (this.options.evalJS && this.isSameOrigin() && contentType 
           && contentType.match(/^\s*(text|application)\/(x-)?(java|ecma)script(;.*)?\s*$/i)))
         this.evalResponse();
     }
@@ -207,6 +207,15 @@ Ajax.Request = Class.create(Ajax.Base, {
     }
   },
   
+  isSameOrigin: function() {
+    var m = this.url.match(/^\s*https?:\/\/[^/]*/);
+    return !m || (m[0] == '#{protocol}//#{domain}#{port}'.interpolate({
+      protocol: location.protocol,
+      domain: document.domain,
+      port: location.port ? ':' + location.port : ''
+    }));
+  },
+  
   getHeader: function(name) {
     try {
       return this.transport.getResponseHeader(name) || null;
@@ -282,7 +291,8 @@ Ajax.Response = Class.create({
     if (!json) return null;
     json = decodeURIComponent(escape(json));
     try {
-      return json.evalJSON(this.request.options.sanitizeJSON);
+      return json.evalJSON(this.request.options.sanitizeJSON ||
+        !this.request.isSameOrigin());
     } catch (e) {
       this.request.dispatchException(e);
     }
@@ -295,7 +305,8 @@ Ajax.Response = Class.create({
         this.responseText.blank())
           return null;
     try {
-      return this.responseText.evalJSON(options.sanitizeJSON);
+      return this.responseText.evalJSON(options.sanitizeJSON ||
+        !this.request.isSameOrigin());
     } catch (e) {
       this.request.dispatchException(e);
     }
diff --git a/test/unit/ajax.html b/test/unit/ajax.html
index 1d533ad..3744d34 100644
--- a/test/unit/ajax.html
+++ b/test/unit/ajax.html
@@ -410,6 +410,45 @@
       } else {
         info(message);
       }
+    }},
+    
+    testIsSameOriginMethod: function() {with(this) {
+      var isSameOrigin = Ajax.Request.prototype.isSameOrigin;
+      assert(isSameOrigin.call({ url: '/foo/bar.html' }), '/foo/bar.html');
+      assert(isSameOrigin.call({ url: window.location.toString() }), window.location);
+      assert(!isSameOrigin.call({ url: 'http://example.com' }), 'http://example.com');
+
+      if (isRunningFromRake) {
+        Ajax.Request.prototype.isSameOrigin = function() {
+          return false
+        };
+
+        $("content").update('same origin policy');
+        new Ajax.Request("/response", extendDefault({
+          parameters: Fixtures.js,
+          onComplete: function(transport) { 
+            assertEqual("same origin policy", $("content").innerHTML);
+          }
+        }));
+
+        new Ajax.Request("/response", extendDefault({
+          parameters: Fixtures.invalidJson,
+          onException: function(request, error) {
+            assert(error.message.include('Badly formed JSON string'));
+          }
+        }));
+
+        new Ajax.Request("/response", extendDefault({
+          parameters: { 'X-JSON': '{});window.attacked = true;({}' },
+          onException: function(request, error) {
+            assert(error.message.include('Badly formed JSON string'));
+          }
+        }));
+
+        Ajax.Request.prototype.isSameOrigin = isSameOrigin;
+      } else {
+        info(message);
+      }
     }}
   });
 // ]]>