_Theft of Service_ could be significant as malicious users could get access to sensitive data within the chip. For example, Satellite TV is a kind of IoT node that is directly connected to the service provider. An attacker could modify security to gain free services, which could cause huge losses to the service provider. In addition, _cloning and IP Piracy_ is a notorious challenge faced by the electronic industry today. Various gadgets get cloned in the industry through physical attacks by getting internal memory contents such as device ID, unique keys, etc. Due to this, not only development cost is avoided but also the sellers of these cloned device receive a significant amount of profit. This practice is unlawful since they use the intellectual property of a company who already invested time and money.  
_Denial of Service_ can be used as an attack by devices to satisfy selfish motives. For example, IoT nodes can be easily reverse-engineered to send fake data to deceive the destination server.  
These physical attacks can introduce huge threats not only to customers but also to the companies that are bound to protect people's personal data. Now, these physical attacks can happen through standard hardware interfaces such as USB, JTAG, LAN, WLAN, Serial interface, etc.  
JTAG [4] is an IEEE standard developed in the 1990s for debugging, updating and storing firmware on the chip and still this standard is widely used in the industry. Usually, IoT nodes are small embedded devices that have a program that runs continuously in a loop called firmware. These application programs are directly written into the chip through either serial or JTAG debugging interface. Manufacturers keep JTAG port on PCB board to test/validate if every single electronic part is appropriately mounted or not, as well as for upgrading the firmware in the future. There are many JTAG debuggers available in the market which cost from ten to a few hundred dollars, which makes it even easier for attackers to get access to the internals of a chip and firmware. If we consider this scenario with thousands of sensor IoT devices, then product manufacturing companies need to provide not only secure data transmission between multiple devices but also should be more resilient against physical theft and the intellectual property of the device. Moreover, the IoT business model is not only about one time product selling but also includes monthly/yearly service subscription model such as TV channel subscriptions, Google assistant services, etc. This paper studies how JTAG port access to hardware could be severe and huge in terms of IoT endpoints nodes that are less complex, battery operated, accessible to the public and importantly those will be in millions of numbers. This paper covers both various exploitation of products through JTAG port and previous proposed solutions that make JTAG access secured.  
This paper is further organized as follows. In Section 2, we describe the basic background of JTAG IEEE 1149.1 standard. Section 3 includes various JTAG exploitations that have been demonstrated before from commercial products to industrial products. Section 4 contains different methods that have been proposed to make JTAG interface secure. Section 5 provides the discussion of the topic and Section 6 gives the conclusion and future insight in terms of JTAG interface and IOT infrastructure.