Recently, Man in the Middle (MitM) attacks on web browsing have become easier than they have ever been before because of a problem called "Name Collision" and a protocol called the Web Proxy Auto-Discovery (WPAD) protocol. This name collision attack can cause all web traffic of an Internet user to be redirected to a MitM proxy automatically right after the launching of a standard browser. The underlying problem of this attack is internal namespace WPAD query leakage, which itself is a known problem for years. However, it remains understudied since it was not easily exploitable before the recent new gTLD (generic Top-Level Domains) delegation. In this paper, we focus on this newly-exposed MitM attack vector and perform the first systematic study of the underlying problem causes and its vulnerability status in the wild. First, we show the severity of the problem by characterizing leaked WPAD query traffic to the DNS root servers, and find that a major cause of the leakage problem is actually a result of settings on the end user devices. More specifically, we find that under common settings, devices can mistakenly generate internal queries when used outside an internal network (e.g., used at home). Second, we define and quantify a candidate measure of attack surface by defining "highly-vulnerable domains", which are domains routinely exposing a large number of potential victims, and use it to perform a systematic assessment of the vulnerability status. We find that almost all leaked queries are for new gTLD domains we define to be highly-vulnerable, indirectly validating our attack surface definition. We further find that 10% of these highly-vulnerable domains have already been registered, making the corresponding users immediately vulnerable to the exploit at any time. Our results provide a strong and urgent message to deploy proactive protection. We discuss promising directions for remediation at the new gTLD registry, Autonomous System (AS), and end user levels, and use empirical data analysis to estimate and compare their effectiveness and deployment difficulties.