TLS protocol is an essential part of secure Internet communication. In past, many attacks have been identified on the protocol. Most of these attacks are due to flaws in protocol implementation. The flaws are due to improper design and implementation of program logic by programmers. One of the widely used implementation of TLS is SChannel which is used in Windows operating system since its inception. We have used "protocol state fuzzing" to identify vulnerable and undesired state transitions in the state machine of the protocol for various versions of SChannel. The client as well as server components have been analyzed thoroughly using this technique and various flaws have been discovered in the implementation. Exploitation of these flaws under specific circumstances may lead to serious attacks which could disrupt secure communication. In this paper, we analyze state machine models of TLS protocol implementation of SChannel library and describe weaknesses and design flaws in these models, found using protocol state fuzzing.

Abstract-Attacks in cyberspace have got attention due to risk at privacy, breach of trust and financial losses for individuals as well as organizations. In recent years, these attacks have become more complex to analyze technically, as well as to detect and prevent from accessing confidential data. Although there are many methodologies and mechanisms which have been suggested for cyber-attack detection and prevention, but not from the perspective of an attacker. This paper presents the cyberdefence as hindrances, faced by the attacker, by understanding attack thread and defence possibilities with existing security mechanisms. Seven phases of Cyber Attack Thread are introduced and technical aspects are discussed with reference to APT attacks. The paper aims for security practitioner and administrators as well as for the general audience to understand the attack scenario and defensive security measures.