Exploit-DB #43937
Description: WebKit - 'detachWrapper' Use-After-Free
Type: dos
Platform: multiple
Date: 2018-02-01
Author: Google Security Research

Exploit:
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There is a use-after-free security vulnerability in WebKit. The vulnerability was confirmed on ASan build of Revision 225572 on OSX.

The PoC is attached.

Preliminary Analysis:

SVGPropertyTearOff keeps a pointer to a SVG property in m_value. When detachWrapper() is called, that pointer gets dereferenced and the value copied. This comment explains when/why this is used
https://github.com/WebKit/webkit/blob/5277f6fb92b0c03958265d24a7692142f7bdeaf8/Source/WebCore/svg/properties/SVGPropertyTearOff.h#L105
SVGPropertyTearOff keeps track of just a single value. In case the SVG property is actually a list of values, the values are stored in a Vector and SVGPropertyTearOff will keep a pointer to somewhere inside the vector's buffer. If a vector gets resized before detachWrapper() is called and the vector's buffer gets realloc()'ed, SVGPropertyTearOff's m_value will point to freed memory.


ASan log:

=================================================================
==50494==ERROR: AddressSanitizer: heap-use-after-free on address 0x60c0000dccc0 at pc 0x0001262c1ba0 bp 0x7ffeee3a0460 sp 0x7ffeee3a0458
READ of size 8 at 0x60c0000dccc0 thread T0
==50494==WARNING: invalid path to external symbolizer!
==50494==WARNING: Failed to use and restart external symbolizer!
    #0 0x1262c1b9f in WebCore::SVGPropertyTearOff<WebCore::SVGLengthValue>::detachWrapper() (/Users/projectzero/webkit/WebKit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0xfe2b9f)
    #1 0x1263e58ba in WebCore::SVGListProperty<WebCore::SVGLengthListValues>::detachListWrappersAndResize(WTF::Vector<WebCore::SVGLength*, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc>*, unsigned int) (/Users/projectzero/webkit/WebKit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x11068ba)
    #2 0x12899fc77 in void WebCore::SVGAnimatedTypeAnimator::executeAction<WebCore::SVGAnimatedListPropertyTearOff<WebCore::SVGLengthListValues> >(WebCore::SVGAnimatedTypeAnimator::AnimationAction, WTF::Vector<WebCore::SVGElementAnimatedProperties, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc> const&, unsigned int, WebCore::SVGAnimatedListPropertyTearOff<WebCore::SVGLengthListValues>::ContentType*) (/Users/projectzero/webkit/WebKit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x36c0c77)
    #3 0x128985a0e in WebCore::SVGAnimateElementBase::resetAnimatedType() (/Users/projectzero/webkit/WebKit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x36a6a0e)
    #4 0x128afacc2 in WebCore::SVGSMILElement::progress(WebCore::SMILTime, WebCore::SVGSMILElement*, bool) (/Users/projectzero/webkit/WebKit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x381bcc2)
    #5 0x128af82c1 in WebCore::SMILTimeContainer::updateAnimations(WebCore::SMILTime, bool) (/Users/projectzero/webkit/WebKit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x38192c1)
    #6 0x128af6b5c in WebCore::SMILTimeContainer::timerFired() (/Users/projectzero/webkit/WebKit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x3817b5c)
    #7 0x127f21112 in WebCore::ThreadTimers::sharedTimerFiredInternal() (/Users/projectzero/webkit/WebKit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x2c42112)
    #8 0x127fc6009 in WebCore::timerFired(__CFRunLoopTimer*, void*) (/Users/projectzero/webkit/WebKit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore:x86_64+0x2ce7009)
    #9 0x7fff3e602bb3 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ (/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation:x86_64h+0x8ebb3)
    #10 0x7fff3e602826 in __CFRunLoopDoTimer (/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation:x86_64h+0x8e826)
    #11 0x7fff3e602329 in __CFRunLoopDoTimers (/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation:x86_64h+0x8e329)
    #12 0x7fff3e5f992a in __CFRunLoopRun (/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation:x86_64h+0x8592a)
    #13 0x7fff3e5f8d22 in CFRunLoopRunSpecific (/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation:x86_64h+0x84d22)
    #14 0x7fff3d910e25 in RunCurrentEventLoopInMode (/System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/HIToolbox:x86_64+0x2fe25)
    #15 0x7fff3d910b95 in ReceiveNextEventCommon (/System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/HIToolbox:x86_64+0x2fb95)
    #16 0x7fff3d910913 in _BlockUntilNextEventMatchingListInModeWithFilter (/System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/HIToolbox:x86_64+0x2f913)
    #17 0x7fff3bbdbf5e in _DPSNextEvent (/System/Library/Frameworks/AppKit.framework/Versions/C/AppKit:x86_64+0x41f5e)
    #18 0x7fff3c371b4b in -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] (/System/Library/Frameworks/AppKit.framework/Versions/C/AppKit:x86_64+0x7d7b4b)
    #19 0x7fff3bbd0d6c in -[NSApplication run] (/System/Library/Frameworks/AppKit.framework/Versions/C/AppKit:x86_64+0x36d6c)
    #20 0x7fff3bb9ff19 in NSApplicationMain (/System/Library/Frameworks/AppKit.framework/Versions/C/AppKit:x86_64+0x5f19)
    #21 0x7fff6611a42e in _xpc_objc_main (/usr/lib/system/libxpc.dylib:x86_64+0x1042e)
    #22 0x7fff66119081 in xpc_main (/usr/lib/system/libxpc.dylib:x86_64+0xf081)
    #23 0x10185d4d6 in main (/Users/projectzero/webkit/WebKit/WebKitBuild/Release/WebKit.framework/Versions/A/XPCServices/com.apple.WebKit.WebContent.xpc/Contents/MacOS/com.apple.WebKit.WebContent.Development:x86_64+0x1000014d6)
    #24 0x7fff65e4d114 in start (/usr/lib/system/libdyld.dylib:x86_64+0x1114)

0x60c0000dccc0 is located 0 bytes inside of 128-byte region [0x60c0000dccc0,0x60c0000dcd40)
freed by thread T0 here:
    #0 0x1239d4fa4 in __sanitizer_mz_free (/Applications/Xcode.app/Contents/Devel