Exploit-DB #42360
Description: WebKit - 'WebCore::AccessibilityNodeObject::textUnderElement' Use-After-Free
Type: dos
Platform: multiple
Date: 2017-07-24
Author: Google Security Research

Exploit:
<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1249

There is a use-after-free security vulnerability in WebKit. The vulnerability was confirmed on ASan build of WebKit nightly.

Note that accessibility features need to be enabled in order to trigger this bug. On Safari on Mac this can be accomplished by opening the inspector (simply opening the inspector enables accessibility features). On WebKitGTK+ (and possibly other WebKit releases) accessibility features are enabled by default.

PoC:

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-->

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ASan log:

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==728==ERROR: AddressSanitizer: heap-use-after-free on address 0x[PII_REDACTED]a0 at pc 0x000109f2cbb5 bp 0x7fff5e08a430 sp 0x7fff5e08a428
READ of size 8 at 0x[PII_REDACTED]a0 thread T0
==728==WARNING: invalid path to external symbolizer!
==728==WARNING: Failed to use and restart external symbolizer!
    #0 0x109f2cbb4 in WebCore::AccessibilityNodeObject::textUnderElement(WebCore::AccessibilityTextUnderElementMode) const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x25bb4)
    #1 0x109f58273 in WebCore::AccessibilityRenderObject::textUnderElement(WebCore::AccessibilityTextUnderElementMode) const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x51273)
    #2 0x109f2a6e0 in WebCore::accessibleNameForNode(WebCore::Node*, WebCore::Node*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x236e0)
    #3 0x109f2e8d3 in WebCore::AccessibilityNodeObject::accessibilityDescriptionForElements(WTF::Vector<WebCore::Element*, 0ul, WTF::CrashOnOverflow, 16ul>&) const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x278d3)
    #4 0x109f2ec3e in WebCore::AccessibilityNodeObject::ariaLabeledByAttribute() const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x27c3e)
    #5 0x109f279c9 in WebCore::AccessibilityNodeObject::ariaAccessibilityDescription() const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x209c9)
    #6 0x109f2ed5c in WebCore::AccessibilityNodeObject::hasAttributesRequiredForInclusion() const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x27d5c)
    #7 0x109f5d550 in WebCore::AccessibilityRenderObject::computeAccessibilityIsIgnored() const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x56550)
    #8 0x109f464ab in WebCore::AccessibilityObject::accessibilityIsIgnored() const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x3f4ab)
    #9 0x10a0e2df1 in WebCore::AXObjectCache::getOrCreate(WebCore::RenderObject*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x1dbdf1)
    #10 0x10a0e0b6f in WebCore::AXObjectCache::getOrCreate(WebCore::Node*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x1d9b6f)
    #11 0x10a0e650d in WebCore::AXObjectCache::textChanged(WebCore::Node*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x1df50d)
    #12 0x10a820041 in WebCore::Element::attributeChanged(WebCore::QualifiedName const&, WTF::AtomicString const&, WTF::AtomicString const&, WebCore::Element::AttributeModificationReason) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x919041)
    #13 0x10a826268 in WebCore::Element::didAddAttribute(WebCore::QualifiedName const&, WTF::AtomicString const&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x91f268)
    #14 0x10a82607c in WebCore::Element::addAttributeInternal(WebCore::QualifiedName const&, WTF::AtomicString const&, WebCore::Element::SynchronizationOfLazyAttribute) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x91f07c)
    #15 0x10a81f8d7 in WebCore::Element::setAttributeInternal(unsigned int, WebCore::QualifiedName const&, WTF::AtomicString const&, WebCore::Element::SynchronizationOfLazyAttribute) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x9188d7)
    #16 0x10a81f6c1 in WebCore::Element::setAttribute(WTF::AtomicString const&, WTF::AtomicString const&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x9186c1)
    #17 0x10b463b93 in WebCore::jsElementPrototypeFunctionSetAttributeCaller(JSC::ExecState*, WebCore::JSElement*, JSC::ThrowScope&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x155cb93)
    #18 0x10b4555d8 in long long WebCore::BindingCaller<WebCore::JSElement>::callOperation<&(WebCore::jsElementPrototypeFunctionSetAttributeCaller(JSC::ExecState*, WebCore::JSElement*, JSC::ThrowScope&)), (WebCore::CastedThisErrorBehavior)0>(JSC::ExecState*, char const*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x154e5d8)
    #19 0x10b455441 in WebCore::jsElementPrototypeFunctionSetAttribute(JSC::ExecState*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x154e441)
    #20 0x279e6e001027  (<unknown module>)
    #21 0x115e2934a in llint_entry (/Users/projectzero/webkit/webkit/WebKitBuild/Release/JavaScr