Apple WebKit: Type confusion in RenderBox with accessibility enabled CVE-2017-2373 There is a type confusion vulnerability that affects WebKit with accessibility enabled (WebCore::AXObjectCache::gAccessibilityEnabed). PoC: =============================== foo
=============================== Bad cast happens in RenderBox.h in inline RenderBox* RenderBox::firstChildBox() const { return downcast(firstChild()); } The function expects that the first child is going to be of type RenderBox, but in the PoC it is actually of type RenderText. This was tested on WebKitGTK+ 2.14.2 (latest stable version at this time). The PoC also crashes Safari on Mac, but only if the PoC is run while the Web Inspector / Error Console are enabled. It appears this behavior is caused by the fact that opening inspector enables accessibility features (via a call to AXObjectCache::enableAccessibility), while accessibility features are enabled in WebKitGTK+ by default through WebPageAccessibilityObjectAtk. ASAN log follows. ================================================================= ==5530==ERROR: AddressSanitizer: global-buffer-overflow on address 0x7fd724fdca78 at pc 0x7fd72289499f bp 0x7ffc9e7a40b0 sp 0x7ffc9e7a40a8 READ of size 8 at 0x7fd724fdca78 thread T0 #0 0x7fd72289499e in WebCore::RenderBox::computeBlockDirectionMargins(WebCore::RenderBlock const&, WebCore::LayoutUnit&, WebCore::LayoutUnit&) const /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBox.cpp:3260:21 #1 0x7fd7228a00b1 in WebCore::RenderBox::computeAndSetBlockDirectionMargins(WebCore::RenderBlock const&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBox.cpp:3270:5 #2 0x7fd7227faa45 in WebCore::RenderBlockFlow::layoutBlockChild(WebCore::RenderBox&, WebCore::RenderBlockFlow::MarginInfo&, WebCore::LayoutUnit&, WebCore::LayoutUnit&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:660:5 #3 0x7fd7227f6abe in WebCore::RenderBlockFlow::layoutBlockChildren(bool, WebCore::LayoutUnit&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:632:9 #4 0x7fd7227f2d55 in WebCore::RenderBlockFlow::layoutBlock(bool, WebCore::LayoutUnit) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:487:9 #5 0x7fd7227a24b7 in WebCore::RenderBlock::layout() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlock.cpp:1075:5 #6 0x7fd7227fb3a0 in WebCore::RenderBlockFlow::layoutBlockChild(WebCore::RenderBox&, WebCore::RenderBlockFlow::MarginInfo&, WebCore::LayoutUnit&, WebCore::LayoutUnit&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:709:9 #7 0x7fd7227f6abe in WebCore::RenderBlockFlow::layoutBlockChildren(bool, WebCore::LayoutUnit&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:632:9 #8 0x7fd7227f2d55 in WebCore::RenderBlockFlow::layoutBlock(bool, WebCore::LayoutUnit) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:487:9 #9 0x7fd7227a24b7 in WebCore::RenderBlock::layout() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlock.cpp:1075:5 #10 0x7fd7227fb3a0 in WebCore::RenderBlockFlow::layoutBlockChild(WebCore::RenderBox&, WebCore::RenderBlockFlow::MarginInfo&, WebCore::LayoutUnit&, WebCore::LayoutUnit&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:709:9 #11 0x7fd7227f6abe in WebCore::RenderBlockFlow::layoutBlockChildren(bool, WebCore::LayoutUnit&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:632:9 #12 0x7fd7227f2d55 in WebCore::RenderBlockFlow::layoutBlock(bool, WebCore::LayoutUnit) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:487:9 #13 0x7fd7227a24b7 in WebCore::RenderBlock::layout() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlock.cpp:1075:5 #14 0x7fd7227fb3a0 in WebCore::RenderBlockFlow::layoutBlockChild(WebCore::RenderBox&, WebCore::RenderBlockFlow::MarginInfo&, WebCore::LayoutUnit&, WebCore::LayoutUnit&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:709:9 #15 0x7fd7227f6abe in WebCore::RenderBlockFlow::layoutBlockChildren(bool, WebCore::LayoutUnit&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:632:9 #16 0x7fd7227f2d55 in WebCore::RenderBlockFlow::layoutBlock(bool, WebCore::LayoutUnit) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlockFlow.cpp:487:9 #17 0x7fd7227a24b7 in WebCore::RenderBlock::layout() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlock.cpp:1075:5 #18 0x7fd722c7d92f in WebCore::RenderView::layoutContent(WebCore::LayoutState const&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderView.cpp:244:5 #19 0x7fd722c7ee64 in WebCore::RenderView::layout() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderView.cpp:370:9 #20 0x7fd72221b17b in WebCore::FrameView::layout(bool) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/page/FrameView.cpp:1438:9 #21 0x7fd721495fe2 in WebCore::Document::updateLayout() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/dom/Document.cpp:2007:9 #22 0x7fd7214a2801 in WebCore::Document::updateLayoutIgnorePendingStylesheets(WebCore::Document::RunPostLayoutTasks) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/dom/Document.cpp:2039:5 #23 0x7fd721579993 in WebCore::Element::innerText() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/dom/Element.cpp:2518:5 #24 0x7fd720c6d821 in WebCore::accessibleNameForNode(WebCore::Node*, WebCore::Node*) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/accessibility/AccessibilityNodeObject.cpp:1887:16 #25 0x7fd720c7695c in WebCore::AccessibilityNodeObject::accessibilityDescriptionForElements(WTF::Vector&) const /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/accessibility/AccessibilityNodeObject.cpp:1930:44 #26 0x7fd720c77102 in WebCore::AccessibilityNodeObject::ariaLabeledByAttribute() const /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/accessibility/AccessibilityNodeObject.cpp:1955:12 #27 0x7fd720c773e9 in WebCore::AccessibilityNodeObject::ariaAccessibilityDescription() const /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/accessibility/AccessibilityNodeObject.cpp:1166:28 #28 0x7fd720c773e9 in WebCore::AccessibilityNodeObject::hasAttributesRequiredForInclusion() const /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/accessibility/AccessibilityNodeObject.cpp:1963 #29 0x7fd720cc408b in WebCore::AccessibilityRenderObject::computeAccessibilityIsIgnored() const /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/accessibility/AccessibilityRenderObject.cpp:1356:9 #30 0x7fd720cac82c in WebCore::AccessibilityObject::accessibilityIsIgnored() const /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/accessibility/AccessibilityObject.cpp:2978:19 #31 0x7fd720cab793 in WebCore::AccessibilityObject::notifyIfIgnoredValueChanged() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/accessibility/AccessibilityObject.cpp:2870:22 #32 0x7fd72279df02 in WebCore::RenderBlock::makeChildrenNonInline(WebCore::RenderObject*) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlock.cpp:707:5 #33 0x7fd72279d37a in WebCore::RenderBlock::addChildIgnoringContinuation(WebCore::RenderObject*, WebCore::RenderObject*) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBlock.cpp:606:9 #34 0x7fd722eb34fa in WebCore::RenderTreePosition::insert(WebCore::RenderObject&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/style/RenderTreePosition.h:93:5 #35 0x7fd722eb34fa in WebCore::RenderTreeUpdater::createRenderer(WebCore::Element&, WebCore::RenderStyle&&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/style/RenderTreeUpdater.cpp:370 #36 0x7fd722eaec96 in WebCore::RenderTreeUpdater::updateElementRenderer(WebCore::Element&, WebCore::Style::ElementUpdate&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/style/RenderTreeUpdater.cpp:283:9 #37 0x7fd722eac9ad in WebCore::RenderTreeUpdater::updateRenderTree(WebCore::ContainerNode&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/style/RenderTreeUpdater.cpp:173:9 #38 0x7fd722eabdcf in WebCore::RenderTreeUpdater::commit(std::unique_ptr >) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/style/RenderTreeUpdater.cpp:120:9 #39 0x7fd7214a045e in WebCore::Document::recalcStyle(WebCore::Style::Change) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/dom/Document.cpp:1936:13 #40 0x7fd7214a1a4f in WebCore::Document::updateStyleIfNeeded() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/dom/Document.cpp:1982:5 #41 0x7fd7214a1a4f in WebCore::Document::implicitClose() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/dom/Document.cpp:2807 #42 0x7fd721f666e8 in WebCore::FrameLoader::checkCallImplicitClose() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/loader/FrameLoader.cpp:870:5 #43 0x7fd721f666e8 in WebCore::FrameLoader::checkCompleted() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/loader/FrameLoader.cpp:816 #44 0x7fd721f6101a in WebCore::FrameLoader::finishedParsing() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/loader/FrameLoader.cpp:737:5 #45 0x7fd7214da906 in WebCore::Document::finishedParsing() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/dom/Document.cpp:5228:9 #46 0x7fd721c66aca in WebCore::HTMLDocumentParser::end() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/html/parser/HTMLDocumentParser.cpp:406:5 #47 0x7fd721c66aca in WebCore::HTMLDocumentParser::attemptToRunDeferredScriptsAndEnd() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/html/parser/HTMLDocumentParser.cpp:415 #48 0x7fd721c66aca in WebCore::HTMLDocumentParser::prepareToStopParsing() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/html/parser/HTMLDocumentParser.cpp:135 #49 0x7fd721f480d3 in WebCore::DocumentWriter::end() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/loader/DocumentWriter.cpp:269:5 #50 0x7fd721f20e29 in WebCore::DocumentLoader::finishedLoading(double) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/loader/DocumentLoader.cpp:442:5 #51 0x7fd721f2a031 in WebCore::DocumentLoader::continueAfterContentPolicy(WebCore::PolicyAction) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/loader/DocumentLoader.cpp:829:13 #52 0x7fd721f25361 in WebCore::DocumentLoader::responseReceived(WebCore::CachedResource*, WebCore::ResourceResponse const&) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/loader/DocumentLoader.cpp:711:9 #53 0x7fd721f1b2a9 in WebCore::DocumentLoader::handleSubstituteDataLoadNow() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/loader/DocumentLoader.cpp:477:5 #54 0x7fd722434521 in WebCore::ThreadTimers::sharedTimerFiredInternal() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/platform/ThreadTimers.cpp:121:9 #55 0x7fd71f10ff1b in WTF::RunLoop::TimerBase::TimerBase(WTF::RunLoop&)::$_3::operator()(void*) const /home/ifratric/webkit/webkitgtk-2.14.2/Source/WTF/wtf/glib/RunLoopGLib.cpp:162:9 #56 0x7fd71f10ff1b in WTF::RunLoop::TimerBase::TimerBase(WTF::RunLoop&)::$_3::__invoke(void*) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WTF/wtf/glib/RunLoopGLib.cpp:160 #57 0x7fd717fcf059 in g_main_context_dispatch (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x4a059) #58 0x7fd717fcf3ff (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x4a3ff) #59 0x7fd717fcf721 in g_main_loop_run (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x4a721) #60 0x7fd71f10f384 in WTF::RunLoop::run() /home/ifratric/webkit/webkitgtk-2.14.2/Source/WTF/wtf/glib/RunLoopGLib.cpp:94:9 #61 0x7fd7208b6f98 in int WebKit::ChildProcessMain(int, char**) /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebKit2/Shared/unix/ChildProcessMain.h:61:5 #62 0x7fd71378b82f in __libc_start_main /build/glibc-GKVZIf/glibc-2.23/csu/../csu/libc-start.c:291 #63 0x41a218 in _start (/webkit/libexec/webkit2gtk-4.0/WebKitWebProcess+0x41a218) 0x7fd724fdca78 is located 272 bytes to the right of global variable 'vtable for WebCore::RenderText' defined in '/home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderText.cpp' (0x7fd724fdc400) of size 1384 SUMMARY: AddressSanitizer: global-buffer-overflow /home/ifratric/webkit/webkitgtk-2.14.2/Source/WebCore/rendering/RenderBox.cpp:3260:21 in WebCore::RenderBox::computeBlockDirectionMargins(WebCore::RenderBlock const&, WebCore::LayoutUnit&, WebCore::LayoutUnit&) const Shadow bytes around the buggy address: 0x0ffb649f38f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0ffb649f3900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0ffb649f3910: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0ffb649f3920: 00 00 00 00 00 00 00 00 00 00 00 00 00 f9 f9 f9 0x0ffb649f3930: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 =>0x0ffb649f3940: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9[f9] 0x0ffb649f3950: f9 f9 f9 f9 f9 f9 f9 f9 00 00 00 00 00 00 f9 f9 0x0ffb649f3960: f9 f9 f9 f9 00 00 00 00 00 00 00 00 00 00 00 00 0x0ffb649f3970: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0ffb649f3980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0ffb649f3990: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 Shadow byte legend (one shadow byte represents 8 application bytes): Addressable: 00 Partially addressable: 01 02 03 04 05 06 07 Heap left redzone: fa Heap right redzone: fb Freed heap region: fd Stack left redzone: f1 Stack mid redzone: f2 Stack right redzone: f3 Stack partial redzone: f4 Stack after return: f5 Stack use after scope: f8 Global redzone: f9 Global init order: f6 Poisoned by user: f7 Container overflow: fc Array cookie: ac Intra object redzone: bb ASan internal: fe Left alloca redzone: ca Right alloca redzone: cb ==5530==ABORTING 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. Found by: ifratric